# Maxing CO2 in Low Techs



## frothhelmet

Co2 in a low tech | UK Aquatic Plant Society

What this thread means to me is that low tech tanks should do even better (get more CO2) in general when they have more opportunities for gas exchange with the atmosphere. Maybe we should try some wet/dry trickle filters on a lowtech and see the plant growth results...


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## BigTom

Yeah we've discussed this a little bit in a couple of threads, but I'll be darned if I can find them. The general feeling from a few of us low-techers was that maintaining an equilibrium level of CO2 through having shallow tanks, lots of surface movement or wet/dry trickle filters was a better approach than - or at least a reasonable alternative to - the classic Walstad idea of minimal water changes and low flow in order to conserve CO2 produced from the substrate, with the added advantages that you can also discard the notion of avoiding water changes if desired, and the extremely stable CO2 levels mean the tanks are even more robust to certain forms of algae.

Furthermore, it means that O2 levels are similarly stable, which can only be a good thing for fish health (directly and by keeping the filter bacteria happy). Finally, shallow tanks and trickle filters also allow ample opportunity for emersed and riparian planting, which again help maintain a stable environment and good water quality.


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## a1Matt

I don't know where those threads are lurking either.

I believe adding a wet\dry for this purpose has merit (it is on my list of things to try at some point in the future - probably via a sump).

The furthest I've taken it is having a high flow rate and making sure that my spray bar creates as much surface movement as possible.


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## BigTom

Some discussion here - Starting up on the fresher side of fishkeeping. | Page 2 | UK Aquatic Plant Society

And here - Low tech lighting levels | Page 3 | UK Aquatic Plant Society


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## BigTom

And at the risk of self-promotion, I think Alastair and myself have demonstrated that the shallow method works pretty well -


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## Nathaniel Whiteside

BigTom said:


> And at the risk of self-promotion, I think Alastair and myself have demonstrated that the shallow method works pretty well -



Surface to water Ratio is key I reckon.


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## BigTom

Nathaniel Whiteside said:


> Surface to water Ratio is key I reckon.


 

I certainly think it is for these tanks. A good trickle filter should give comparable results though, I would think, if paired with appropriate flow through the tank.


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## Nathaniel Whiteside

BigTom said:


> I certainly think it is for these tanks. A good trickle filter should give comparable results though, I would think, if paired with appropriate flow through the tank.



Yes, there's something very appealing to me about a trickle. Maybe I'm just a kid and would like the waterfall effect. 

Would be ideal for growing flora In the top basket!


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## OllieNZ

A DeBruyn filter would be ideal for that.


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## sciencefiction

I won't be posting pictures because my tank isn't scaped with such finesse but Tom's and Alistair's method works in a normally shaped tank too, at least in my 5f and a small 7g tank.
According to "scientists"  , in *still* water it takes 6 years for oxygen to diffuse to a depth of 6 meters. So imagine if you've got a tank with no surface movement at all like in an old fashioned "Walstad" tank where this was not recommended at all...These tanks rely hugely on organics decomposition by bacteria for CO2 production which in turn is a massive oxygen consumer in order to do so. Plants do produce oxygen, but they consume it too and 99% of everything else that lives in the tanks consumes oxygen as well so you want as much as possible O2 in a low tech to keep it healthy.

I think that's why the large surface area combined with surface movement works great for Tom and Alistair. But it works in a normal shape tank as long as you do provide surface movement for gas diffusion.

On a side note, I've applied the same tactic over the years on a normal inert substrate planted low techs, loads of filtration and surface movement and no algae either. These are my observations but it works each time if you invest in heavy filtration and setup good circulation around the tank. However, it works way better with soil because the inert substrate doesn't seem to be able to store nutritients as well and plants show defficiencies despite algae never appearing.


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## foxfish

I think we still remember the our fist planted tanks from years back, the concept of keeping the co2 in the tank rather than gassing it off.. it worked very well too.
Now we have a new angle but, I have yet to be convinced myself!
I have read Darrel's post & understand what he is saying but like yourself I don't really get it LOL


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## Andy Thurston

foxfish said:


> I think we still remember the our fist planted tanks from years back, the concept of keeping the co2 in the tank rather than gassing it off.. it worked very well too.
> Now we have a new angle but, I have yet to be convinced myself!
> I have read Darrel's post & understand what he is saying but like yourself I don't really get it LOL



I think your bang on here foxfish. I dont think you will be convinced till you try it yourself and see


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## BigTom

I used to run zero flow _a la_ Walstad on my tank, and while plenty of plant species grew really well I did have trouble with some. Glosso, for example, only ever grew upwards and predictably died off in the end. I've now tried again and have glosso happily carpeting along the front. Although I've changed the lighting and substrate since the last attempt, light levels, water chemistry and water change rate seem to be broadly comparable to before, with the only major change has been the addition of flow and a lot of surface movement.

Just a small example, but I do think it makes a difference for some plants.


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## Tim Harrison

A glosso carpet in a low-tech is pretty impressive Tom.

I can't quite get my head around the veeery slow rate of atmospheric CO2 diffusion in to water and plant demand...surely demand would soon outstrip supply...regardless of surface area : volume ratio and trickle filters etc...


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## dw1305

Hi all,





Troi said:


> I can't quite get my head around the veeery slow rate of atmospheric CO2 diffusion in to water and plant demand...surely demand would soon outstrip supply...regardless of surface area : volume ratio and trickle filters etc...


 No it doesn't, CO2 is actually quite soluble in water, so even though there is only ~400ppm in the atmosphere if you have a large enough diffusion surface you can get the levels of CO2 fairly close to equilibrium values. The other great thing about a large gas exchange surface is that it is a negative feedback circuit, when the concentration gradient is steep, gas will diffuse in/out more quickly, as levels approach equilibrium rates slow.

The same applies to oxygen as CO2, but with the difference that you have a lot more in the atmosphere (22%), but O2 is a lot less soluble in water than CO2. I'll stick with dissolved oxygen, but by definition the same processes apply to all gases that have differing concentrations at the gas exchange surface.

If you use pollution as your measure of oxygen demand (so we are talking about BOD, Biochemical Oxygen Demand) you can ameliorate a huge bioload with a trickle filter. This is a waste water example, but landfill leachate and sewage are really just uber-polluted tank water <http://water.me.vccs.edu/courses/ENV149/trickling.htm>. 





> High-rate trickling filters have been used advantageously for pre-treatment of industrial wastes and unusually strong wastewaters. When so used they are called "roughing filters". With these filters the BOD loading is usually in excess of 110 pounds of BOD per 1000 cubic feet of filter medium. Generally, most organic wastes can be successfully treated by trickling filtration. Normally food processing, textile, fermentation and some pharmaceutical process wastes are amenable to trickling filtration.


 If I'm not talking to the converted, I'd add plants into the equation. I think people should have access to this paper <http://www.feng.unimas.my/ujce/images/article/volume12013/paper%203encrypted.pdf>, and it has an interesting take on a free self-produced filter media (unless you are thinning on top like me).

Biological filtration capacity is a measure of oxygen exchange, and what applies to oxygen also applies to the other atmospheric gases. You can maximize gas diffusion in various ways, including having laminar flow <Feature Article: Water Flow is More Important for Corals Than Light, Part V — Advanced Aquarist | Aquarist Magazine and Blog> which is very effective, but technically more difficult than having a large gas exchange surface in the filter. If you have a wide shallow tank you have advantages in terms of area to volume ratio, but deep tanks can still be aerated by laminar flow, as long as you have enough water turn over.

cheers Darrel


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## Tim Harrison

Good old air pollution...increasing the concentration of atmospheric CO2...there's always a silver lining...somewhere

Thanks for the papers...they are very interesting, as you say what goes for O2 goes for other gases too and especially CO2 because it's more water soluble than O2. And I also understand what you're saying about the parallels between the filters meeting BOD and therefore also being able to meet plant demand for CO2.

So for dissolved CO2 to remain constant the filter volume would have to be a function of aquarium volume and the density of the plant mass. So taking that in to account along with a realistic carbon affinity for a hypothetically typical macrophyte, etc do you reckon it'd be possible to arrive at a rough formula for calculating trickle filter size? Note I added an etc in there in case I've missed something crucial so it looks like I actually know what I'm talking about  I suppose realistically there are just too many unquantifiable variables to do it justice, but given our preference for densely planted tanks don't you think the filter would have to be quite large though?

Aside from that am I right in thinking water in equilibrium with air contains 0.5 mg/l CO2? If this is so, is it entirely possible - in soil substrate tanks at least with higher concs of CO2 due to decomposition - that trickle filters and tanks with large surface area:volume ratios are actually degassing CO2 to achieve equilibrium?


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## sciencefiction

I am repeating myself but I think Diana Walstad's original idea of having no surface movement was to preserve the CO2 produced in the substrate by decomposition of organics via *oxygen* consumation. This bacteria is aerobic! She also said that the CO2 amount produced is *higher* than the one via surface movement diffusion and that's what many folks don't understand.   However she first advised to eliminate surface movement in order to prevent diffusion of CO2 in air, but she recently advised she's changed her mind, and advised for surface movement and means of oxygenation explaining that it's the oxygen those tanks are having problem with. It's way less solubale in water than CO2 but it's essential for decomposition of organics, so low oxygen, low CO2 at the end of the day. Without enough oxygen, there's not enough CO2 production, plants suffer, the substrate goes anaerobic, that leads to even less oxygen, bad bacteria flourishes, fish die.  She said that especially at the start, when the soil is full of organics, this can lead to a dead tank pretty fast. Imagine also an old Walstad tank where organics have been piling up in the substrate for months and years, same thing. Oxygen is the key and I agree with Darrel on that as he pointed it out many times.
In a high tech that's not an issue because one scrubs the tanks clean several times a week as per the advise here as well


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## sciencefiction

> Aside from that am I right in thinking water in equilibrium with air contains 0.5 mg/l CO2? If this is so, is it entirely possible - in soil substrate tanks at least with higher concs of CO2 due to decomposition - that trickle filters and tanks with large surface area:volume ratios are actually degassing CO2 to achieve equilibrium?


 
From what I understand equilibrium refers to the saturation of gasses at surface area but levels of gasses below that area are totally different story. So basically in a Walstad tank there will be low CO2 concentrations at the surface(equilibrium), but the deeper it goes, the higher concentrations of CO2, the highest being near the substrate where the decomposition occurs which is constant as long as there's enough O2. So plants always have a chance to consume CO2 on time.
However, the O2 is the opposite story, the highest concentrations will be near the surface and rapidly decrease the deeper the tank. If one has no surface movement, then no oxygen enters via equilibrium(as it takes 6 years for 6 meters in still water) Tom and Alistairs tanks are shallow with big surface area and surface movement, therefore oxygen gets down to that substrate where the aerobic bacteria consums it in high rates in order to decompose organics and produce CO2. You need aerobic bacteria decomposition, not anaerobic, So it's the O2 you need worrying about. Temperature is also a key factor to O2. And obviously, everything in a tank competes for oxygen, from decomposition bacteria, to nitrogen bacteria to fish and plants when they don't photosynthesise.

Obviously in a lightly stocked tank, well planted with careful feeding one may get away with no surface movement if the soil is not rich in organics as plants produce O2 as well, but the more O2, the better.


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## Tim Harrison

For me surface movement, flow and distribution, and regular and substantial water changes are key. Degassing from trickle filters is something else altogether, and high surface area to volume ratio will also accelerate the process.


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## sciencefiction

Troi said:


> For me surface movement, flow and distribution, and regular and substantial water changes are key. Degassing from trickle filters is something else altogether, and high surface area to volume ratio will also accelerate the process.



  But if you call it oxygenation instead of degassing it takes a different meaning.
  CO2 gets produced 24 hours a day in a Walstad tank in the substrate and via fish respiration.  CO2 requirement by plants is majorly needed during the light period of 7-8 hrs a day max. So even with some diffusion, there'll be enough left for the plants if you promote faster CO2 production than it can be lost by diffusion.
 Oxygen comsumation on another hand is a 24/7 requirement and is vital not just for fish, but for plants methabolism and CO2 production by bacteria.   Oxygen in a non-surface movement tank gets produced just during the light period by plants for 7-8 hours a day. So no back up there.   Oxygen is less soluble in water and harder to retain in water.   When you run low on oxygen CO2 production slows down as well, plants growth and methabolism slow down, so why pointing out CO2 degassing as an issue when you wouldn't be promoting plant health, fish health, tank stability and CO2 production in the first place via oxygenation.
 So personally, I don't see why a shallow tank would be a disadvantage as it promotes better oxygenation, and in turn more CO2 and better plant health.  I don't see how trickle filters can be a disadvantage but I think the means of directing the flow to reach all around the tank is as important and trickle filters are a bit tricky that way


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## dw1305

Hi all, 





Troi said:


> Good old air pollution...increasing the concentration of atmospheric CO2


 Up from about 300ppm pre-industrial revolution, and often higher in than 400 ppm in well insulated houses. 





Troi said:


> So taking that in to account along with a realistic carbon affinity for a hypothetically typical macrophyte, etc do you reckon it'd be possible to arrive at a rough formula for calculating trickle filter size?


 Probably not a formula, quite small trickle filters have the potential to deal with a lot of BOD, but in that case it is slightly different from CO2, as the wet surfaces in the filter contain the nitrifying bacteria and are using atmospheric oxygen. The CO2 they produce is out-gassed straight to the atmosphere. 





Troi said:


> Aside from that am I right in thinking water in equilibrium with air contains 0.5 mg/l CO2? If this is so, is it entirely possible - in soil substrate tanks at least with higher concs of CO2 due to decomposition - that trickle filters and tanks with large surface area:volume ratios are actually degassing CO2 to achieve equilibrium?


 Quite likely, and it doesn't have to be a soil substrate tank for this to happen, any tank with a high plant load is going to have CO2 levels build up at night, unless we take measures to out-gas it. This is actually another advantage as it stops your fish asphyxiating at night. The details for the dissolution of CO2 ar here: <http://www.pwtag.org/researchdocs/Used%20Ref%20docs/52%20Carbondioxide%20in%20water%20equilibrium.pdf>. 





sciencefiction said:


> She also said that the CO2 amount produced is higher than the one via surface movement diffusion and that's what many folks don't understand. However she first advised to eliminate surface movement in order to prevent diffusion of CO2 in air, but she recently advised she's changed her mind, and advised for surface movement and means of oxygenation explaining that it's the oxygen those tanks are having problem with. It's way less solubale in water than CO2 but it's essential for decomposition of organics, so low oxygen, low CO2 at the end of the day. Without enough oxygen, there's not enough CO2 production, plants suffer, the substrate goes anaerobic, that leads to even less oxygen, bad bacteria flourishes, fish die


 I think this is a pretty good summary of where we are. I also think you need to factor dKH into this as well, Diana Walstad is using a carbonate rich substrate because nitrification uses both O2 and carbonates. 





sciencefiction said:


> Oxygen is the key and I agree with Darrel on that as he pointed it out many times.


Yes that is really it, I'm not really interested in the levels of CO2 in my tanks, and I know that they will change dramatically during the photo-period, all I have to do is keep the oxygen levels high, have some nutrients (including CO2) and everything is OK.

cheers Darrel


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## Bufo Bill

Hi, I've been reading this with great interest, and find what Darrel is saying makes a lot of sense to my mind. I do have one very simple question, however; can you give me examples of carbonate rich substrates? No great theoretical questions, I just don't know what these substrates are!
All the best from Bill.


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## BigTom

Bufo Bill said:


> Hi, I've been reading this with great interest, and find what Darrel is saying makes a lot of sense to my mind. I do have one very simple question, however; can you give me examples of carbonate rich substrates? No great theoretical questions, I just don't know what these substrates are!
> All the best from Bill.


 

I've never actually read Walstad, but I think in this case it just refers to the fact that the commercial soil mixes favoured in this sort of approach tend to contain limestone, which is a ready source of calcium carbonate.


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## dw1305

Hi all,





BigTom said:


> I've never actually read Walstad


 Go on buy a copy, every-one should own one, only £9.59 for the Kindle version. It is a bit like reading Richard Dawkins you might not agree 100% with all of findings, but 99.9% of them are pure gold dust and it is a fantastic book <Amazon.co.uk: Diana Walstad: Books, Biogs, Audiobooks, Discussions>. 





Bufo Bill said:


> can you give me examples of carbonate rich substrates?





BigTom said:


> but I think in this case it just refers to the fact that the commercial soil mixes favoured in this sort of approach tend to contain limestone, which is a ready source of calcium carbonate.


 Pretty much, in her book she says 





> "for softwater tanks then I would advise hobbiests to use a soil that contains a source of hard water nutrients. Acidic garden soils can be fertilized with powdered dolomite lime.......for fertilizing potting soils I would use a less reactive lime source such as pelleted dolomitic lime, oyster grit or crushed sea shell"


In much of the S. and E. of the UK the soil will naturally be carbonate rich, although most of our limestones haven't undergone dolomitization (where some of the calcium carbonate is replaced by magnesium carbonate).
She likes hard water tanks because they maintain a more stable pH (personally I'm not too bothered about pH fluctuation, but she doesn't change much water, so acidification over time is more of a problem), they provide calcium, magnesium etc. and also keep any heavy metals as insoluble carbonates or hydroxides.

The book also has some figures for the extent and duration of carbon release (as CO2) from soils (on page 83).

cheers Darrel


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## Andy Thurston

I need to read the rest of this. I put it down after reading a third of it and suffering with information overload.
Does anybody know if there are any differences between the 1st, 2nd and 3rd editions


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## BigTom

dw1305 said:


> Hi all, Go on buy a copy, every-one should own one, only £9.59 for the Kindle version. It is a bit like reading Richard Dawkins you might not agree 100% with all of findings, but 99.9% of them are pure gold dust and it is a fantastic book <Amazon.co.uk: Diana Walstad: Books, Biogs, Audiobooks, Discussions>.


 

Perhaps you have convinced me. I'll add it to the list for Santa.


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## Tim Harrison

It's a good reference and quite accessible without too much prior knowledge...I read it in one sitting but not sure how much actually went in though.



Big clown said:


> I need to read the rest of this. I put it down after reading a third of it and suffering with information overload.
> Does anybody know if there are any differences between the 1st, 2nd and 3rd editions


 
I think the 2nd ed has a few colour plates at the beginning. Not sure about the 3rd ed.


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## Tim Harrison

Thought I'd put my spare drop checker in my low-energy tank just out of curiosity this is the result below 1hr after lights on - after a 4hr siesta period. I'd say it was "insufficient" on the colour chart...but I'm surprised it registered at all in a low-energy tank...


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## OllieNZ

Troi said:


> Thought I'd put my spare drop checker in my low-energy tank just out of curiosity this is the result below 1hr after lights on - after a 4hr siesta period. I'd say it was "insufficient" on the colour chart...but I'm surprised it registered at all in a low-energy tank...


Have you got a ph meter Troi? I would be interested to see a record of hourly ph changes


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## dw1305

Hi all, 





OllieNZ said:


> Have you got a ph meter Troi? I would be interested to see a record of hourly ph changes


 I've never done it systematically, but in my rain-water tanks with light stocking, a reasonable amount of filtration and very heavy planting, the pH varies from about pH6.5 just before lights  on to about pH8 in the middle of the light period. I don't know what the dKH is, but they are about 60 - 70ppm TDS. I assume this pH change relates entirely to the varying proportions of CO2 and O2.

cheers Darrel


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## Tim Harrison

My low-energy tank pH doesn't change much. The tap water round these 'ere parts it's rock 'ard...possibly the hardest water in the UK so it's buffered to kingdom come - but that's the south east for you. It ranges from 7.4-7.6. Obviously the water in the checker is 4dKH solution.

Come to think of it it doesn't change that much in my high-energy tank either...well not like Darrel's low-energy tanks anyway...about 7.2-6.4, and that's with pH lowering substrate as well.


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## dw1305

Hi all, 





Troi said:


> Come to think of it it doesn't change that much in my high-energy tank either...well not like Darrel's low-energy tanks anyway...about 7.2-6.4, and that's with pH lowering substrate as well


 That is the answer, it is just the carbonate buffering. The more dKH (H+ ion acceptors) you have the more stable the pH will be, unless you add a huge amount of acids (H+ ion donors). In the case of adding CO2, only a small amount of the CO2 will become carbonic acid (H2C03) and you need to add a lot of CO2 to drive the CO2~ HCO3 equilibrium in favour of H2CO3 and reduce the pH.

This is one of the problems with discussing pH with other fish keepers, if they keep marine fish, or Lake Tanganyika cichlids, they are dealing with systems where pH is virtually immobile, and it needs a huge change in water chemistry to change the pH. In very soft low TDS water the opposite is true, and even the additions of small amounts of weak acids (H2CO3) and bases (O2) will dramatically alter the pH. 

This is partially why the whole mythology of "pH crashes" have built up and it is so difficult to persuade people that pH reduction and fish death are both symptoms of underlying bio-acidification <Bio-acidification | The Skeptical Aquarist> and acidosis, rather than the former having caused the latter.  

cheers Darrel


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## GreenNeedle

Trouble with the Walstad book is that even Diana now uses circulation pumps or powerhead etc in her tanks.

I run all my non CO2 tanks these days with a 10% weekly water change.  Each with circa 1.2WPG LED.  No major algae problems.  The odd little bit of BBA or dusting on rocks but thats it.

Similarly on a previous scape of mine I got bored with it after 6 months (was a hitec, CO2, setup) I lowered the light amount, turned off CO2, stopped regular dosing and it didn't get a water change for 14 months.  Fish waste and food was the main source of nutrient and I just added a pinch of KN03 and KH2PO4 if I noticed GSA developing.  That was probably every 2 months or so.  Filter turnover was only 5.6x and I always like to have a ripple on the surface.

This was the last photo as a hi tec in August 2009.  Mark Evans took this photograph so it maybe looks a bit better 




And 13 months later (haven't got a 14month photo. lol) with no water changes since August 2009.  Here is the same tank in September 2010  slightly overrun with cherry shrimp and MTS but still healthy:




Further on in February 2011.  Same tank still alive.




All in all it had full CO2 hi tec treatment for the first 5 months and then for a one month period after the 14 months of water change then back to non CO2.


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## Nathaniel Whiteside

SuperColey1 said:


> Trouble with the Walstad book is that even Diana now uses circulation pumps or powerhead etc in her tanks.
> 
> I run all my non CO2 tanks these days with a 10% weekly water change.  Each with circa 1.2WPG LED.  No major algae problems.  The odd little bit of BBA or dusting on rocks but thats it.
> 
> Similarly on a previous scape of mine I got bored with it after 6 months (was a hitec, CO2, setup) I lowered the light amount, turned off CO2, stopped regular dosing and it didn't get a water change for 14 months.  Fish waste and food was the main source of nutrient and I just added a pinch of KN03 and KH2PO4 if I noticed GSA developing.  That was probably every 2 months or so.  Filter turnover was only 5.6x and I always like to have a ripple on the surface.
> 
> This was the last photo as a hi tec in August 2009.  Mark Evans took this photograph so it maybe looks a bit better
> 
> 
> 
> 
> And 13 months later (haven't got a 14month photo. lol) with no water changes since August 2009.  Here is the same tank in September 2010  slightly overrun with cherry shrimp and MTS but still healthy:
> 
> 
> 
> 
> Further on in February 2011.  Same tank still alive.
> 
> 
> 
> 
> All in all it had full CO2 hi tec treatment for the first 5 months and then for a one month period after the 14 months of water change then back to non CO2.




How did you find that poppy inlet? Just out of interest.


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## oldbloke

Seeing as CO2 is heavier than air, would it be a good idea to leave a small amount of space above the waterline so any CO2 released could sit on the surface of the water?


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## Tim Harrison

Ok then this is the colour of the drop checker first thing before lights on...it's pretty much approaching "normal" CO2 levels, which by anyone's standards it pretty darn good for a low-energy, soil substrate tank. Again 4dKH solution...However, I can't comment on long-term consistency...at the moment...and maybe I should confirm the readings with another drop checker to make sure.


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## dw1305

oldbloke said:


> Seeing as CO2 is heavier than air, would it be a good idea to leave a small amount of space above the waterline so any CO2 released could sit on the surface of the water?


 No, you are going to lose much more CO2 via diffusion into the air. Ideally you want bubbles that are as small as possible, with as longer retention time as possible in the water column.

cheers Darrel


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## oldbloke

dw1305 said:


> No, you are going to lose much more CO2 via diffusion into the air. Ideally you want bubbles that are as small as possible, with as longer retention time as possible in the water column.
> 
> cheers Darrel


 
Thanks Darrel.
I ain't got no bubbles at all as I've gone back to low tech!!! 
It's just that I worked with CO2 in one way or another for a number of years and suddenly thought about it laying as a blanket on the top of the water.


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## GreenNeedle

Nathaniel Whiteside said:


> How did you find that poppy inlet? Just out of interest.


 
It's fine.  no problems.  bought it in 2007


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## oldbloke

Troi said:


> Oh...I sorta misunderstood before...I think...


 
Well, if it sat there and if a little was absorbed, it's all going to help, I guess?


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## Nathaniel Whiteside

oldbloke said:


> Well, if it sat there and if a little was absorbed, it's all going to help, I guess?



Where are you from OB?

On your flickr, you have pictures of bluebell wood, which looks very much like blue bell woods located in Richmond, North Yorkshire.


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## oldbloke

Different bluebell wood mate, but originally from a brewing town about 50 miles down the A1.....


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## faizal

Wow,..so many technical stuffs here.....these are new to me. So ,...the new way to go for low tech  ( i.e.  to increase our chances of growing a nice carpet of crypt parva or e. tenellus or saggitaria subulata) would be to make sure that we have the following?

1. A nice wide shallow tank 
2. Lots of surface movements
3. wet/dry trickle filter to increase the co2 concentration within the water column. ???

This will enable us to grow carpets??? Did i get this right?

Can we run an airline with O2 during the lights out period for say 3-5 hrs to increase the chances of gaseoeus exchange with the environment or will this turn out to be counter productive as it might gas out the nocturnal accumulation of co2? It really shouldn't matter right ? ...because  if we have a trickle filter,....the gasses are gonna get gassed out anyways ....right? I am so confused now


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## dw1305

Hi all, 





faizal said:


> This will enable us to grow carpets??? Did i get this right?


 I think Tom and Alastair have had success with carpets, I've never had any joy at the bottom of the tank, but my tanks are always jungles, so I don't really have any suitable spaces. _Hemianthus_ did fine for me on top off an HMF sponge, but had access to aerial CO2. 





faizal said:


> Can we run an airline with O2 during the lights out period for say 3-5 hrs to increase the chances of gaseoeus exchange with the environment or will this turn out to be counter productive as it might gas out the nocturnal accumulation of co2? It really shouldn't matter right ? ...because if we have a trickle filter,....the gasses are gonna get gassed out anyways ....right?


That's right, we are aiming to have a large gas exchange surface to volume ratio, so that levels of all dissolved gases more closely follow the atmospheric levels at all times.There is a good page on dissolved gases here: <Aquatic Chemistry>.

This method differs from Diana Walstad's initial idea that you could have an organic rich sediment that produced CO2 (from the oxidisation of OM), and then minimal water movement retained this in the water column. I'm a great fan of hers, but I don't think this is a viable technique, mainly because you are likely to end up with problems with low oxygen levels outside of the photo-period. 

I'm more than willing to trade any night-time build up of CO2 (and loss of DO.) for high(er) oxygen levels during the night.

The combination of heavily planted tanks, constant high levels  of oxygenation, and regular water changes, mean that you can maintain very clean water with minimal BOD. This will lead to sub-optimal plant growth, but you can then use the "Duckweed Index" <Low maintainence, long term sustrate | UK Aquatic Plant Society> to maintain some plant growth.

There is a more complete explanation of this in: <plecoplanet: Aeration and dissolved oxygen in the aquarium> I wrote this specifically for keepers of rheophilic plecs, but it is relevant for most fish keeping.

These are KISS solutions to aquarium maintenance.

cheers Darrel


----------



## BigTom

Funny this thread got bumped, I'm right in the middle of a little trial to see what effect shutting off the flow/surface movement has on the pH (as a proxy for CO2) in my tank. On the second day of monitoring pH with the usual flow setup, if it agrees roughly with yesterday's results I'll shut off the filter at lights out tonight and see if it makes a change tomorrow.

As for carpets, I've had far more luck with flow then without, although it still seems pretty hit and miss as to which species do well (_Lilleaopsis_ is a safe bet, and _Glossostigma_ is doing OK this time with flow).


----------



## roadmaster

I run Hydro sponge filter's at night on timer in low tech heavily planted tank's.
Some argue that plant's should provide enough O2 during the day, to carry the plant's,fishes O2 requirement;s for evening but I have seen no harm from supplying a bit more O2 through exchange at surface via the sponge filter's at night ,so I continue. 
Fishes/plant's thrive.


----------



## BigTom

I just did an experiment, sort of. I've stated a couple of times previously purely on the basis of intuition that I reckoned a shallow tank like mine with a reasonable amount of flow would probably be fairly good at keeping CO2 levels somewhere around equilibrium.

So I measured pH at regular intervals throughout the day for two days, and then to see what effect flow was having I unattached my filter completely and ran the tank without a filter for the next 2 days. Readings were taken from the exact same spot and depth in the tank (an area of open water near the center of the tank, halfway down the water column) using a Hanna 98129 meter which was calibrated once at the beginning of the experiment.

Assuming a constant alkalinity and not too much drift on the pH meter, the change in pH should predominantly reflect changes in the concentration of CO2 in the water. I realise this is a simplified interpretation, but please correct me if I've got it completely wrong.

Here are the results (photoperiod designated by orange bars) -






Here's the same data expressed in terms of estimated CO2 levels relative to the maximum estimate observed, assuming a stable KH and everything else that might effect pH readings! (I don't have a KH test so can't give actual units):





So what does this show? Well firstly it appears that even with a shallow tank and a reasonable amount of flow and surface ripple there is still quite a strong diurnal fluctuation in pH (CO2), with the estimated CO2 level nearly halving between lights on and lights off.

Secondly switching off the flow does appear to increase the amount of CO2 available, but the plants didn't seem to use that much more of it.

Caveats: I've probably got something totally wrong; this is only a short term experiment so it's hard to say how things might change if I left the filter off; do plants take a while to adjust to increased CO2 availability?

Anyway, I'm not exactly suffering from a lack of plant growth so the filter will be going back on in the morning, but I thought people might be interested. If anything this has got me thinking about increasing surface movement as it demonstrates how hard it is to maintain stable levels of dissolved gasses and O2 is far less soluble than CO2.

And now to bed! I shall look forward to waking up to seeing Darrel and Ceg have replied and pointed out that I'm talking all kinds of gibberish


----------



## dw1305

Hi all, 
Brilliant. Looking at the cluster of points I don't think you need to run the experiment any longer. I think you are right, in that the pH changes are directly attributable to the changing oxygen/CO2 ratio.

cheers Darrel


----------



## Andy Thurston

It does make me wonder if you ran the experiment, with filter off, for longer how much further ph would fall.
How about testing tank water thats been stood to find the datum 


Andys 60l cube | UK Aquatic Plant Society
Andys HC propagator step by step | UK Aquatic Plant Society
Juwel 180 first planted tank | UK Aquatic Plant Society
Rio 125 wood and moss | UK Aquatic Plant Society


----------



## faizal

BigTom said:


> ....
> So what does this show? Well firstly it appears that even with a shallow tank and a reasonable amount of flow and surface ripple there is still quite a strong diurnal fluctuation in pH (CO2), with the estimated CO2 level nearly halving between lights on and lights off.
> 
> Secondly switching off the flow does appear to increase the amount of CO2 available, but the plants didn't seem to use that much more of it.


 
So,...Tom,...does this mean that we :

1). should still go for a wide shallow tank

2).  maintain just a mild to moderate flow in the tank like a pump rated 5-8 times the tank volume per hour (i.e. not   10 times the tank volume turn over rate)

3) make sure that the surface ripple is kept at a minimum

4) Ensure proper distribution of flow throughout the tank (i.e. spraybar along the back glass of the tank / strategically placed lily pipes etc?

5) We can still use the trickle filter to enhance the gaseous exchange ability provided by the shallow tank?

I really want to give this idea a shot y'know?. I've already ordered for a tank 36 inches long, 22 inches deep , 15.5 inches in height . I sort of calculated the surface area per volume ratio (S.A.P.V.R) of Alastair's puddle & these figures brings me close that .....probably off by 0.01 or so I think.


----------



## faizal

Troi said:


> Thought I'd put my spare drop checker in my low-energy tank just out of curiosity this is the result below 1hr after lights on - after a 4hr siesta period. I'd say it was "insufficient" on the colour chart...but I'm surprised it registered at all in a low-energy tank...


 
Troi,.. could you be kind enough to show how much of a surface ripple you have there in this tank please?


----------



## dw1305

Hi all, 





faizal said:


> make sure that the surface ripple is kept at a minimum


 I'm not sure, if you had a trickle filter it would be pretty efficient at out-gassing the CO2 what-ever else you do. My suspicion would be that the differences that Tom recorded are at least partly to do with the degree of oxygen saturation, rather than purely the reflecting a higher level of CO2 with the filter off. The reason I think this is that the shapes of the curves, with filter on and off, are both pretty similar. I think if you were getting  a lot more dissolved CO2 with the filter off, you would have a much more "peaky" curve in that state. 

I'll have a go over the weekend with a pH meter (on a standard 60cm long x 30 wide x 45 high). The tank will start with much softer water than Tom's and will be equally heavily planted.

If they aren't in use I'll borrow a lab. standard DO meter as well. 

cheers Darrel


----------



## BigTom

dw1305 said:


> I think if you were getting a lot more dissolved CO2 with the filter off, you would have a much more "peaky" curve in that state.


 

That's what I was expecting to see. I must admit I hadn't really considered the role of oxygen in all this - my understanding was that it's effect on pH was relatively small compared to CO2, have I got that wrong? I had been wondering if the similarity in the graph shapes was due to the plants actually being limited by light or nutrients, rather than CO2, or perhaps that they required some time to adjust to altering levels of CO2 that are different to what they normally encounter day to day? Unfortunately my understanding of both chemistry and plant physiology falls over at this point.


----------



## BigTom

faizal said:


> So,...Tom,...does this mean that we :
> 
> 1). should still go for a wide shallow tank
> 
> 2). maintain just a mild to moderate flow in the tank like a pump rated 5-8 times the tank volume per hour (i.e. not 10 times the tank volume turn over rate)
> 
> 3) make sure that the surface ripple is kept at a minimum
> 
> 4) Ensure proper distribution of flow throughout the tank (i.e. spraybar along the back glass of the tank / strategically placed lily pipes etc?
> 
> 5) We can still use the trickle filter to enhance the gaseous exchange ability provided by the shallow tank?
> 
> I really want to give this idea a shot y'know?. I've already ordered for a tank 36 inches long, 22 inches deep , 15.5 inches in height . I sort of calculated the surface area per volume ratio (S.A.P.V.R) of Alastair's puddle & these figures brings me close that .....probably off by 0.01 or so I think.


 

Faizal there's no way I would want to try and pass something off as a conclusive answer with the meager data at hand, and I'm not sure I even concluded anything from the tests other than that no flow = lower pH. I think your tank has really nice dimensions and it should be possible to produce very good results with it. With my shallow tank I've had success both with and without flow. Many plants seem to do fine with zero flow, but with trickier ones such as glosso I've definitely had more success with flow. I also think that plants are generally the easy part and worry more about my livestock, so would err towards maximising O2 via plenty of surface movement and/or a trickle filter. I like the wide steady flow that my spraybar gives so would recommend one of those also.

It may not provide maximal CO2, but it seems to be fine for these style of tanks.


----------



## Tim Harrison

faizal said:


> Troi,.. could you be kind enough to show how much of a surface ripple you have there in this tank please?


 
Hi Faizal, I have the spray bar near the surface slightly angled up so there is a fair ripple across the surface...although it doesn't necessarily appear so on this image. The tank is 90l and the filter is rated at 1000l/h; it's made by APS so perhaps that should be taken with a slight pinch of salt. However, you can see  the tall crypts at the back bending to the flow, which should also give you some idea.


----------



## faizal

Troi said:


>


 
sir,...that's one sweet tank . Thank you so much for that picture. The way you guys keep your ferns looking so crunchy nice is way beyond me. Mine always end up looking like i had just stir fried them to bits.


----------



## faizal

dw1305 said:


> Hi all, I'm not sure, if you had a trickle filter it would be pretty efficient at out-gassing the CO2 what-ever else you do. My suspicion would be that the differences that Tom recorded are at least partly to do with the degree of oxygen saturation, rather than purely the reflecting a higher level of CO2 with the filter off.


 
Cheers Darrel. Wow,...this is really complicated isn't it. Never thought that O2 would play a significant role in a tank's pH level.


----------



## faizal

BigTom said:


> I think your tank has really nice dimensions and it should be possible to produce very good results with it.


 
Cheers Tom...it is very comforting to get that approval.



BigTom said:


> ........so would err towards maximising O2 via plenty of surface movement and/or a trickle filter. I like the wide steady flow that my spraybar gives so would recommend one of those also.
> 
> It may not provide maximal CO2, but it seems to be fine for these style of tanks.


 
Tom what's the filtration rate of your filter? Is it 10 times or more?


----------



## BigTom

Um, dunno. It's an Eheim 2323 but probably running at reduced speed because it's pushing water through a very fine filter sock (I get water clarity issues otherwise).

A quick google tells me its rated at 700l/h and I've got a maximum of 200l of water in the tank (probably a bit less), so probably somewhere around 3x turnover.


----------



## ourmanflint

Coming from a reefing background, I'm a little surprised that more people don't use any kind of sump system, where it's possible to "super aerate" the water using a simple skimmer (just using the venturi for aeration not actual skimming). This would definitely maximize CO2 exchange and could be used on a timer to match photo periods if so desired. The added bonus of surface skimming the aquarium via an overflow box, would keep it nice and free of scum, further enhancing gaseous exchange.


----------



## dw1305

Hi all,





ourmanflint said:


> I'm a little surprised that more people don't use any kind of sump system, where it's possible to "super aerate" the water using a simple skimmer (just using the venturi for aeration not actual skimming). This would definitely maximize CO2 exchange and could be used on a timer to match photo periods if so desired.


 I agree. I like as large a gas exchange surface as possible and for that reason I like "wet and dry" trickle filters, although mine used to be over-tank rather than in a sump.

All the details are in this current thread, but have a look here:<Alfagrog for reducing Nitrates? | Page 2 | UK Aquatic Plant Society> for a quicker summary and picture.

I think the main thing for planted tank keepers is that we don't tend to struggle with oxygen levels the way that people with non-planted tanks do. The reasons for this are numerous, but probably the most relevant are that at the end of the photo-period the water will be fully oxygenated, and the plants will have absorbed a lot of the NH3 that otherwise would have entered microbial oxidation. 

Also we differ from marine aquarists in that higher plants have a much higher net productivity than algae like _Chaetomorpha, _or even an "algal scrubber", fresh water holds more oxygen than salt water, and water changes are fairly trouble free and inexpensive for us.

I'm not contemplating going down the salty route, but if I ever did it would be in a system with both a trickle filter and a planted reverse lighting period refugium.

I'm always advocating "_plants as the answe_r", but on Cichlid and Catfish keeping forums a lot of people keep fish that need good oxygenation, but for some reason are adverse to having plants for all sorts of reasons, mainly fairly spurious. That was why I wrote this <plecoplanet: Aeration and dissolved oxygen in the aquarium> (also linked in earlier in the thread).   

cheers Darrel


----------



## roadmaster

Darrel,

I was one of those cichlid,catfish,pleco keeper's.(still am actually)
My effort's at keeping plant's with these fishes were thwarted in large part, by the fishes propensity for digging up substrates and my own ignorance with respect to what plant's were trying to tell me.
I am thank's to folk's here,,largely more successful with the weed's.


----------



## dw1305

Hi all





roadmaster said:


> My effort's at keeping plant's with these fishes were thwarted in large part, by the fishes propensity for digging up substrates


 That is a common one,


> my Pacu, Mbuna, Midas Cichlid, Plec, Koi etc. digs up/eats all my plants


 and it  is true, you do need to physically separate plants and fish, and that isn't always possible within the space available.

cheers Darrel
.


----------



## Jaap

So it is established that gas exchange does good. What would be the best for a low tech no co2 and no liquid carbon tank....aeration, surface agitation or surface skimmer?

Thanks


----------



## frothhelmet

I think it is established that most gas exchange takes place at the surface - so whatever is moving the surface of the water more is going to produce the most gas exchange. Therefore it will depend on which particular set-up you utilise breaks the surface tension and circulates water the most. My vote for most situations would be vigourous aeration.


----------



## Jaap

Anyone else?

Sent from my SM-G900F using Tapatalk


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## dw1305

Hi all, 





Jaap said:


> What would be the best for a low tech no co2 and no liquid carbon tank....aeration, surface agitation or surface skimmer?


 The best technique is probably <"laminar flow">, but I don't think it really matters which route you go down. My suspicion would be that "frothhelmet" is right and that, out of your options, vigorous aeration is the best bet.

What you want is a system that efficiently circulates water to the gas exchange surface.

If  you have direct aeration, via an air pump or venturi, you want very small bubbles with a long retention time in the water column. I like a venturi, partially because you end up with a lot of air bubbles trapped under leaves, and on the filter sponge etc.

Oxygen is fairly slow to diffuse into the water, but CO2 will diffuse more rapidly from trapped air pockets, and a fine leaved plant (or an Amazon Sword etc), may benefit directly from the CO2 trapped at its leaf surface.

There is a more complete answer in: 





dw1305 said:


> <plecoplanet: Aeration and dissolved oxygen in the aquarium>


cheers Darrel


----------



## Jaap

dw1305 said:


> Hi all,  The best technique is probably <"laminar flow">, but I don't think it really matters which route you go down. My suspicion would be that "frothhelmet" is right and that, out of your options, vigorous aeration is the best bet.
> 
> What you want is a system that efficiently circulates water to the gas exchange surface.
> 
> If  you have direct aeration, via an air pump or venturi, you want very small bubbles with a long retention time in the water column. I like a venturi, partially because you end up with a lot of air bubbles trapped under leaves, and on the filter sponge etc.
> 
> Oxygen is fairly slow to diffuse into the water, but CO2 will diffuse more rapidly from trapped air pockets, and a fine leaved plant (or an Amazon Sword etc), may benefit directly from the CO2 trapped at its leaf surface.
> 
> There is a more complete answer in: cheers Darrel



Thanks!

What is a venturi?


----------



## Jaap

Ok I found out what it is.

Now I am confused...

What increases O2 and CO2 levels in a tank? The surface breaking? Doesn't vigorous surface agitation remove CO2 from water? Also, will O2 not increase with an airpump? I mean a venturi blows O2 into the water which presumably will increase O2 levels but will CO2 levels remain the same?


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## chrism

From my understanding...  Surface agitation will increase gas transfer.  So, if your water is higher in CO2 than the air, you will loose CO2 from your water.  However, if your water is lower in CO2 than the air, it will increase the CO2 levels within your water.  

It's the same principle for an airstone only your adding oxygen to the water rather than CO2


Sent from my iPhone using Tapatalk


----------



## dw1305

Hi all, 





chrism said:


> From my understanding... Surface agitation will increase gas transfer. So, if your water is higher in CO2 than the air, you will loose CO2 from your water. However, if your water is lower in CO2 than the air, it will increase the CO2 levels within your water.


 That's it.

The actual dynamics will be different for every tank, mainly because there are a lot of variables (tank surface to volume ratio, water turn over, efficiency of biological filtration, plant mass, fish mass, OM content of the substrate etc.), but the principle is the same.

In a planted tank, during the photo-period, plants are net oxygen producers and CO2 users (when PAR exceeds the <"light compensation point">). During this time period dissolved CO2 will be depleted by photosynthesis, and submerged aquatic plant growth will be carbon limited.

Carbon dioxide will be added to the water by respiration of the bioload and diffusion from the atmosphere at the gas exchange surface, but even in a relatively sparsely planted tank any CO2 will be quickly utilised.

If we increase the area of the gas exchange surface more CO2 will diffuse into the water.

Outside of the photo-period the reverse will happen, CO2 levels will rise and dissolved oxygen will be depleted by the bioload, but if we can get a high enough surface area to volume ratio, levels of *all* dissolved gases in the water will be very similar to the level of atmospheric gases. 

If we aren't adding CO2 this is an advantage for plant growth during the day, and for dissolved oxygen levels at night.

This is also why "wet and dry" trickle filters are so effective for biological filtration, they have a huge gas exchange surface area. 

There is a good discussion of dissolved gases in <"FAO: Aeration and oxygenation in aquaculture"> and at Wikipedia  <"Water aeration">.

cheers Darrel


----------



## Soilwork

So if we encourage high oxygen levels in our non co2 tanks via surface agitation it would make sense that bacterial breakdown of rich soil sediments would be maximised.  Some of the Co2 produced in this manner would/could still be utilised by plants before it has a chance to reach atmosphere?  Or would we reach a point where co2 is off gassing faster than it is being produced.  Surely the plants would still get some of the co2 produced via bacterial activity?


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## EdwinK

As you probably know CO2 level in atmosphere is more than 300 ppm so by good surface agitation you are encouraging not only O2 but CO2 as well. It is way more significant than from bacterial brakedown.


----------



## Soilwork

How much co2? About 0.5ppm? That's not significant at all.


----------



## sciencefiction

EdwinK said:


> As you probably know CO2 level in atmosphere is more than 300 ppm so by good surface agitation you are encouraging not only O2 but CO2 as well. It is way more significant than from bacterial brakedown.



I would dispute the "way more significant" part of this statement......Do you have any scientific data to support this theory, i.e. surface agitation provides more usable co2 to plants than that from the breakdown of organics?
In practice you can blow as much surface agitation as you like and you won't achieve the same amount of healthy growth as in a planted tank with organic soil, even if you dump all your dry ferts into the tank trying to help it. There are reasons why co2 is considered so precious. It goes out as fast as it enters via surface agitation. But plants can take it via the roots in the soil where it is trapped after being produced by microbial activity. A recently planted tank with organic soil "bubbles" with co2.

The surface agitation is always about oxygen, not about co2. O2 is harder to dissolve but stays in the water longer unlike co2. If surface agitation was able to drive 1/5th of the atmospheric co2 into the water at any given time, even once in a few years, , it would kill all your fish.


----------



## Soilwork

I'm not really disputing the organics vs equilibrium theory just that if we aim for equilibrium levels of co2 this does not mean that plants are not getting co2 via soil breakdown at the same time.


----------



## sciencefiction

_"Higher concentrations of CO 2 in bottom sediments (as a result of microbial activity) are also exploited by some macrophytes (e.g., Isoetes) whereby CO2 in the interstitial sediment water diffuses into the roots and then through gas-filled lacunae to the leaves (Raven et al., 1988)"

Isoetids utilize their roots to take up carbon dioxide from sediment porewater (Wium-Andersen 1971; Søndergaard and SandJensen 1979; Raven et al. 1988), and concomitantly release oxygen from their roots, thus raising sediment redox potential (Wium-Andersen and Andersen 1972; Tessenow and Baynes 1978; Sand-Jensen et al. 1982). Relatively high redox potential (Eh) in porewater near the sediment surface can limit the release of mineral nutrients (e.g., ammonium and phosphate) and redox-sensitive metals (e.g., iron) into the water column (e.g., Mortimer 1941; Wetzel 2001). "
_


----------



## EdwinK

Are we talking about CO2 in gas form or all kind of carbon based compounds that can be consumed by plants?


----------



## EdwinK

Soilwork said:


> How much co2? About 0.5ppm? That's not significant at all.


How much do you think you get from microbiological activity?


----------



## sciencefiction

EdwinK said:


> How much do you think you get from microbiological activity?



I asked a question, you answered with two questions  I think its not about the total co2 that has gone through the system.  It's about co2 being available to plants at any given time without periods of it zeroing out.


----------



## EdwinK

Sorry about two questions at the time. Of course I have no scientific proof it's just a theory.  As is a theory that organic soil provides lots of CO2 available to plants. It provides carbon in organic and non organic compounds that plants find much easier to consume in low dissolved CO2 environment.


----------



## dw1305

Hi all,





Soilwork said:


> So if we encourage high oxygen levels in our non co2 tanks via surface agitation it would make sense that bacterial breakdown of rich soil sediments would be maximised. Some of the Co2 produced in this manner would/could still be utilised by plants before it has a chance to reach atmosphere? Or would we reach a point where co2 is off gassing faster than it is being produced. Surely the plants would still get some of the co2 produced via bacterial activity?


They will, this is the situation you deal with when you work with the re-mediation of organically polluted water (commercial aquaculture, sewage treatment etc), here you have huge BOD, and concurrently a large production of CO2. Work on _Eichornia _has shown that the addition of floating macrophytes can turn a lagoon from a net CO2 producer to a net CO2 sink. (<"Floating Aquatic Macrophytes Can Substantially Offset Open Water CO2 Emissions .....".>)

The more CO2 you have in the water, and the larger the surface to volume ratio (gas exchange surface) is, the faster CO2 will equilibrate with atmospheric levels. Because oxygen is much less soluble than CO2, if you have an organic rich substrate you really need a large gas exchange surface, or you run every risk of asphyxiating your life stock at night.  

Diana Walstad (in <"Ecology of the Planted Aquarium">) has figures from Barko & Smart (1983) ("_The effects of organic matter additions to....._") for the production of CO2 from added sources of organic matter, but the authors found that the growth of submerged aquatic plants was reduced by this carbon addition, although this didn't effect plants that were emergent to the same degree.  

You can have water supplies which are naturally carbon dioxide enriched, <"and they tend to have luxuriant plant growth">, even if they are in low nutrient situations. 





EdwinK said:


> Are we talking about CO2 in gas form or all kind of carbon based compounds that can be consumed by plants?


Scientists make a distinction between the CO2/HCO3- which are "Dissolved Inorganic Carbon" and other carbon compounds "Dissolved (or Total) Organic Carbon" (DOC or TOC).

High levels of TOC usually suppress aquatic plant grow, although some of this effect is likely to be to do with the lower levels of light in tinted water.

cheers Darrel


----------



## Soilwork

Cheers Darrel.  You see, I had a walstad tank that bombed out.  My plants died, algae took over and I lost a couple of fish along the way that where showing signs of rapid breathing.  In fact, i remember losing a fish every couple of weeks in this manner and wonder whether it was all due to low oxygen.  I chose John innes no3 but have read that this soil is not the best of choices.  What's more, it was unmineralised.

I don't really suppose my tap water has high amounts of carbon dioxide and it is termed as very soft by the water board. Sometimes I often wonder whether some of the success stories relating to no co2 tanks are almost 'accidental' in the sense that these people just have really good tap water.

Edit: also I have just installed a spray bar which is aimed slightly at the surface.  Fluid dynamics have improved significantly and I have good sway on my plants. With the extra surface ripple my ph is not falling yet a can visually see an abundance of tiny co2 bubbles all over the tank. My drop checker also remains blue. Does this mean the plants are not getting the dissolved co2?  It's hard to tell as I am also dosing 6ml easy carbo daily.


----------



## rebel

EdwinK said:


> Sorry about two questions at the time. Of course I have no scientific proof it's just a theory.  As is a theory that organic soil provides lots of CO2 available to plants. It provides carbon in organic and non organic compounds that plants find much easier to consume in low dissolved CO2 environment.


Hi Edwin you must mean its a hypothesis. In science, theory means an established idea usually having good quality evidence and usually part of an overall consensus.


----------



## EdwinK

Thanks. As you probably can guess English is not my mother-tongue language so it's very difficult to find correct words for such specific topic.


----------



## dw1305

Hi all,





Soilwork said:


> My plants died, algae took over and I lost a couple of fish along the way that where showing signs of rapid breathing. In fact, i remember losing a fish every couple of weeks in this manner and wonder whether it was all due to low oxygen. I chose John innes no3 but have read that this soil is not the best of choices. What's more, it was unmineralised.


I like lean nutrients, and it could well have been low oxygen. The problem with JI No.3 is that you have a lot of potentially oxidisable material and a nitrogen source (again possibly as ammonia (NH3)).





Soilwork said:


> termed as very soft by the water board


Very soft water could also be a problem as well, even with some water changes you could run out of HCO3- and nitrification would then lead to bio-acidification or "old tank syndrome". This used to be common when I started keeping fish and "aged water" was considered beneficial. I never changed any of the tank water, and used to go through cycles of fish death on a fairly regular basis every 6 months or so.





Soilwork said:


> Sometimes I often wonder whether some of the success stories relating to no co2 tanks are almost 'accidental' in the sense that these people just have really good tap water.


I don't think the chemical composition of the water is that important, people have successful low tech tanks in very hard water ("Akwascape" or "Troi"), soft water ("BigTom" etc) you just need regular water changes and an indication of when plant nutrients are lacking. I've suggested the <"Duckweed Index">, as an indicator of when plants need feeding, mainly because the "Duckweed" isn't CO2 limited.





Soilwork said:


> With the extra surface ripple my ph is not falling yet a can visually see an abundance of tiny co2 bubbles all over the tank. My drop checker also remains blue. Does this mean the plants are not getting the dissolved co2?


They are getting some additional CO2, which will be beneficial to plant growth, but not the level of CO2 that is required to change the pH of the 4dKH solution (indicated by the change of colour in the "bromothymol blue" pH indicator solution).

I'm not a CO2 user, but if I was I wouldn't be aiming for 30ppm CO2, <"10 - 15ppm CO2"> would still be a great increase over atmospheric equilibrium values. 

cheers Darrel


----------



## Soilwork

Thanks for the response.  the tank is actually looking healthy for the first time in a long while. 

With the amount bubbles in there there has to be a decent amount of dissolved co2.  The good thing is that my fish are happier.  When I could achieve a lime green drop checker my ph was 6 or possibly even lower. My swordtail would swim erratically with all fins extended and go in to hiding when I would go near the tank.  Cardinals were also showing signs of fin erosion as well my swordtails.

Now the ph is stable I'm getting the best of both worlds.  I'd like to attempt a no co2 tank again with the newly learned methods of increased surface agitation and better water distribution as well as weekly water changes or maybe even small daily ones such as yourself but the amount of time, money and stress it has caused me getting the tank to where it is now puts me off.


----------



## Parablennius

*Afternoon all*

I hope you don’t mind me resurrecting an old thread but having read this through, I have an idea. Referring to the comments by ourmanflint using skimmers and Darrel about maximising gas exchange, see what you think of this. When I kept marine aquariums I started out using air-driven “Sander” counter flow skimmers driven by the excellent Rena 301 air pumps. These were far more efficient than many gave them credit for if  set up properly and kept in tune, key being maximum “dwell” of the fine air bubbles ( limewood airstone) within the contact tube rather than rapid throughput. I used to extend the tubes to the max possible to increase the dwell time.

Now, they won’t skim in the marine sense but must surely saturate the water with whatever is pumped through them?  In my aquarium the surface water is drawn off, over a weir into a space where the water is heated before being pulled through a 42sq. inch surface HFM, after which it is pumped back into the display. I’m thinking I could rig a skimmer in the heater section, before the filter, which would keep bubbles out of the display. I have no intention of ever using CO2 but wondered if you thought this might be worth a go to increase CO2 as I still have all my old equipment?

Cheers


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## zozo

It doesn't hurt to try.. I got a low tech, with a trickle filter and about less then 2,5 times turnover. Naturaly the CO2 is very minimum. Also thougt a lot about it in how to naturaly increase it.. One day i came up with the, i thought, genius idea to use the co2 from the sump bacteria and pump this back to the tank. Bacteria seems to produce (poop) methane and Co2, so i thought this should accumulate in the sump above the trickle filter. So first tried it with an airpump. The constant noise drove me completely crazy.. Then i thought of an air diffusing venturi at the filter outlet and an airtube to the sump. It all worked, the sumps air got diffused into the water column. But with the venturi i had to significantly increase the turnover to 8 times to make it suck any air.
But the Co2 contents in it and what dissolves in the water is neglectable in both cases. I measured 0.1 pH drop in case one, i case two none, probalby the higher turnover also degases co2 faster.

All fun, but i did cut with the wild goose chase and just leave it to mother nature. You just can't realy force it without a pressurized system.  And the very little things you can do, wont realy make your plants grow so much beter, you wont realy notice much difference. Getting it to an optimum is having patience and let the tank mature and provide it's own wallstad gass.


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## dw1305

Hi all,





Parablennius said:


> When I kept marine aquariums I started out using air-driven “Sander” counter flow skimmers driven by the excellent Rena 301 air pumps. These were far more efficient than many gave them credit for if set up properly and kept in tune, key being maximum “dwell” of the fine air bubbles (limewood airstone) within the contact tube rather than rapid throughput. I used to extend the tubes to the max possible to increase the dwell time.


Yes, size of the bubble, and dwell time, are the important parameter for gas exchange with direct aeration. I think that your idea would work pretty well.

You don't get any more oxygen, or CO2, than the atmospheric equilibrium values, but you replenish (or out-gas) them much more efficiently, so it is about as good as you can get for low tech.

cheers Darrel


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## Bart Hazes

BigTom said:


> <snip> So I measured pH at regular intervals throughout the day for two days, and then to see what effect flow was having I unattached my filter completely and ran the tank without a filter for the next 2 days. <snip>
> 
> View attachment 25694
> 
> <snip>



This reply is to an old post (https://www.ukaps.org/forum/threads/maxing-co2-in-low-techs.29856/page-3#post-330177) that I liked. The two days of data points with filter on are very similar as one would expect if this is the routine operation of the tank. When the filter is switched off CO2 jumps up a lot before lights-on after one day and then makes an even bigger jump the second day. I expect the jumps would increase further until the daily curves become near-identical again. With filter on the CO2 decrease stops around 16:00 when, apparently CO2 has dropped to a point where plant take-up slows enough to match CO2 production. After 1 day without filter this is pushed back to 17:00 and for the second day without filter plant grows at a high pace until 21:00. The last day suggest CO2 is no longer depleted to a point where it curtails growth.

If CO2 take-up is dominated by water-air diffusion then no circulation should give less CO2 uptake, the fact that Tom sees it go up significantly indicates to me that CO2 uptake is dominated by generation within the tank by metabolism of fishes, plants and bacteria. But circulation should not reduce metabolic CO2 generation so what is going on? Do early morning CO2 levels without filter rise above ambient and the circulation stimulates off-gassing of the CO2? That doesn't feel right. Or does higher plant growth during the day generate more oxygen, leading to stronger metabolism during the night and thus more CO2. That would also explain why the early morning level on day 2 is higher than on day 1 because plant growth was still increasing.

Still it remains unclear to me what the driving effect of the filter's presence or absence is. Is it an effect on circulation or is the entire biological filtration component taken out of the equation. If the latter, would removing bacterial metabolism not give less CO2. Maybe not if the filter 'wastes' a lot of oxygen on converting ammonia to nitrate or other processes that don't release CO2. Then that oxygen can be use to produce CO2 by plants, fish, and bacteria that decompose the organics in the soil. Simple experiment, messy to interpret, but something interesting is going on.


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## dw1305

Hi all, 





Bart Hazes said:


> Simple experiment, messy to interpret, but something interesting is going on


Yes it isn't conclusive, because it is just a snap-shot and because we can't measure the level of dissolved gases directly and have to use pH as a proxy of  the CO2/O2 ratio. 

My suspicion was that the differences you see mainly relate to the differing levels of dissolved oxygen.





Bart Hazes said:


> Or does higher plant growth during the day generate more oxygen, leading to stronger metabolism during the night and thus more CO2.


There are just a lot of unknowns. Some of the oxygen used by plants for respiration is from oxygen "stored" in cells and lacunae during photosynthesis. 

The simpler answer would be that the more strongly plants are growing the greater the net production of oxygen is. You can equate biomass production with oxygen production, because during photosynthesis one molecule of oxygen is evolved for every molecule of CO2 incorporated. At light compensation point net oxygen production is nil, but as PAR rises plants are massively oxygen producers as the "extra" CO2 is incorporated into carbohydrates.     

It isn't a massively funded area of research but there are scientists working in this field. Have a look at Pedersen, _et. al _(2013) <"Underwater Photosynthesis of Submerged Plants – Recent Advances and Methods"> _Front Plant Sci_. *4*: 140. 

A further complication is that many aquatic plants have evolved morphological adaptations to distribute oxygen to roots and rhizomes situated in anaerobic substrates. 

This is the rhizome of a lotus (_Nelumbo_ sp.) (from the wonderful, but no longer updated, <"Wayne's World">), showing the gas conducting aerenchyma. 






cheers Darrel


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## AverageWhiteBloke

Interesting read! Couple of questions, firstly, all taken into account here, when would be the best time to perform a water change, before lights come on or after? Just thinking if we have a small amount of co2 built up over night would it be best to let the lighting period have what's there and perform the change after lights out would be more beneficial and the extra oxygen caused by it be better through the night?

Secondly, when it comes to floating plants, keeping a fair amount of them is obviously a good thing for stripping out waste but would having too many floaters reduce the amount of gas exchange interface on the surface?


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## AverageWhiteBloke

Just remembered there was a third question  If we are saying increased o2 then leads to more co2 through increased de-nitrification is there a place in a non co2 setup for those twinstar and similar products which appear to release hydrogen to break algae cell walls which then converts to o2 increasing o2 levels>co2 levels? Maybe that would be behind the claim that they are beneficial in planted aquariums.


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## Matt @ ScapeEasy

Came across this earlier and thought I would try and answer to keep the discussion going on a very interesting topic... strange how some questions never get answered here...



AverageWhiteBloke said:


> Interesting read! Couple of questions, firstly, all taken into account here, when would be the best time to perform a water change, before lights come on or after? Just thinking if we have a small amount of co2 built up over night would it be best to let the lighting period have what's there and perform the change after lights out would be more beneficial and the extra oxygen caused by it be better through the night?
> 
> Secondly, when it comes to floating plants, keeping a fair amount of them is obviously a good thing for stripping out waste but would having too many floaters reduce the amount of gas exchange interface on the surface?



Water changes add co2 and oxygen so its probably more complex that this. I always personally recommend adding glut (liquid co2) during a water change (and only then - nasty chemical overall which does more harm than good https://www.jbl.de/?lang=en&mod=blog&func=detail&id=123) due to its temporary algecide properties as the water change is a "time of change" for the tank good or bad which can allow algae to take hold. I've had good success personally using this strategy.

Floaters I guess would reduce available surface area for gas exchange, yes. Given the success demonstrated here with shallow tanks suspect flow becomes important too (assuming you are  referring to a normal depth tank) to move co2 and/or oxygen rich water from the surface to the depths and present more opportunity for gaseous exchange by moving less co2 and oxygen rich water from the depths back up again.




AverageWhiteBloke said:


> Just remembered there was a third question  If we are saying increased o2 then leads to more co2 through increased de-nitrification is there a place in a non co2 setup for those twinstar and similar products which appear to release hydrogen to break algae cell walls which then converts to o2 increasing o2 levels>co2 levels? Maybe that would be behind the claim that they are beneficial in planted aquariums.



Maybe in low tech systems but in high tech I don't believe they would help raise co2 levels beyond their already elevated position.. the debate will rage on with these units I think!... I also suspect that this increased denitrification by filter bacteria thing depends on plant mass and fertilisation and stocking levels... take an extreme example of a non fertilised planted aquarium... There isn't likely going to be enough spare ammonia knocking around for this to have much of an effect as the filter is already dealing with it all.


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## JMorgan

Having just read through this thread, well skimmed through to be honest, I kept noticing the oft repeated statements about dwell time and size of bubbles, small being better etc.
That reminded me of something I saw recently, which is probably very well-known to many here, but which intrigued me, not least because I do love to find an excuse for a little DIY project. 


I think its safe to assume that the amount of lift generated must correspond pretty directly to the size of the bubbles and how 'saturated' the water is within the uplift pipe with air?
Obviously the intent in the video and with normal usage is to make the uplift as efficient as possible, so dwell time is very small, especially since he has this pouring over the top of an HMF. 

I wonder what might happen if, instead of using a vertical pipe, you applied the same idea to a rising spiral tube, thereby considerably increasing dwell time? I think you'd want the outlet to be beneath the surface to avoid it immediately gassing off, and you could even add another venturi to the outlet, as well as disperse the flow force with a spray bar.
With a trickle filter, we're maximising water surface in contact with air, but with tiny bubbles we're maximising air surface in contact with water. I also wonder, without having even the beginnings of the maths and physics to figure it out, how depth and pressure play into this equation?

I have a 60cm cube tank standing empty and a hankering to play with a some _B.smaragdina_ bred by a local chap. I was already thinking of using an HMF with this to give it a nice black back drop and hide the heater, but with this tank I'll want very gentle flow. So it might be a good candidate for sending the return water on a fairly long journey to combine maximising the gas exchange (for the CO2 for the plants - _B.smaragdina_ couldn't care less about the O2) with reducing the strength of flow, whilst still keeping everything moving gently.


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## Matt @ ScapeEasy

Makes sense... see Dennerle CO2 Flipper


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## Edvet

JMorgan said:


> thinking of using an HMF


I love HMF, i run mine on cheap smal filters, either two small ones or a larger one. I use the outflow"pipe" just below the surface angled slightly upward to get some surface movement or just above to break the surface.
These:

 
Very reliable and no sound.


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## dw1305

Hi all,





JMorgan said:


> I think its safe to assume that the amount of lift generated must correspond pretty directly to the size of the bubbles and how 'saturated' the water is within the uplift pipe with air?
> Obviously the intent in the video and with normal usage is to make the uplift as efficient as possible, so dwell time is very small, especially since he has this pouring over the top of an HMF.


Yes, it's the design of the uplift tubes that allows them to efficiently move that much water. 





JMorgan said:


> I wonder what might happen if, instead of using a vertical pipe, you applied the same idea to a rising spiral tube, thereby considerably increasing dwell time?


I don't think it will make much difference, where the surface is broken you get a larger gas exchange area and you move a larger volume of water, so you benefit more from laminar flow. A larger gas exchange surface helps, low tech, by continually replenishing the atmospheric CO2. 





JMorgan said:


> I think you'd want the outlet to be beneath the surface to avoid it immediately gassing off, and you could even add another venturi to the outlet, as well as disperse the flow force with a spray bar.


I don't think you will have enough flow for this.  These are by far the best air-lift designs I've seen. 





JMorgan said:


> how depth and pressure play into this equation?


They do, but it is "_swings and roundabouts_" because the increased pressure reduces the amount of air reaching the bottom of the uplift tube. 





Edvet said:


> I love HMF


They are great filters. 





Edvet said:


> Very reliable and no sound.


That is definitely an advantage of power-heads, over air pumps.

cheers Darrel


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## JMorgan

dw1305 said:


> I don't think it will make much difference, where the surface is broken you get a larger gas exchange area and you move a larger volume of water, so you benefit more from laminar flow. A larger gas exchange surface helps, low tech, by continually replenishing the atmospheric CO2.



Understood, but with a bubble-nesting species I want to keep any water movement very gentle indeed, especially at the surface. Hence the idea to have, on the one hand a fairly efficient uplift to draw water through the matten filter, and then return it almost as inefficiently as possible, to minimise surface disturbance whilst maximising the dwell time of the mini bubbles. While I appreciate that there are more efficient ways of circulating water through an HMF, such as Edvet's suggestion, in this situation the whole idea rests on 'injecting' atmospheric CO2 into the water column. Anyway, this particular application is a very quirky and unusual situation, trying to have one's cake and eat it, and there are many more ways to solve the problem: One I especially like is to raise the height of the up lift and have the water return by trickling down through some hanging planters, dispersing the return and effectively adding a trickle filter to the HMF. Lots of options to play with


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## dw1305

Hi all, 





JMorgan said:


> One I especially like is to raise the height of the up lift and have the water return by trickling down through some hanging planters, dispersing the return and effectively adding a trickle filter to the HMF


I like that one. 

cheers Darrel


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