# Airstones in low tech tanks



## Gfish (21 Oct 2010)

Hi,
I'm aware that having too much surface agitation in a Co2 injected tank is bad and understand the reason, but on a low tech tank is there an advantage to having an airstone, Venturi or excessive surface agitation? I.e over oxygenating.
The reason I ask this is, of the 3 tanks in my house, my daughters 2ft is the healthiest by far. No signs of algae. A bubble curtain along the back wall. Masses of plants some very slow but others fast enough to need a trim every few weeks. And it's never been treated to more than the occasional pour in fertiliser and a weekly 40% waterchange or so.


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## dw1305 (21 Oct 2010)

Hi all,
I'm pretty sure the bubble wall isn't the factor making a difference. The only advantage I can see is that the water in the tank will be fairly well mixed, meaning that the whole water volume will be at, or near, equilibrium with atmospheric CO2 levels. 

In any low tech tank levels of CO2 and O2 will show diurnal variation, with levels of CO2 falling and O2 rising during active photosynthesis and vice-versa during lights off. 

It might be the water change making a difference? they will add NPK (and possibly CO2) if it is tap water?

I only keep low tech tanks, which I both over-filter (with the venturi on) and change "excessive" amounts of water and it is the method that works for me as well.

cheers Darrel


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## Brenmuk (22 Oct 2010)

This is an intriguing question and I don't really know the answer myself   :? . 
I have always aimed to reduce water surface turbulence on the basis of preserving the CO2 already present in my tank.

I have read on various forums that the alkalinity of the tank water can act like a re chargeable battery for CO2, during the lights off period CO2 is stored up (as HCO3-  & CO3--)  and plants can then make use of it during the lights on period when demand for CO2 is highest. So presumably water surface turbulence would reduce the amount of CO2 that gets stored up at night?

But equally in a well planted low tech tank during the lights on period, with minimal turbulence the tank water CO2 concentration would drop below the level reached by equilibrium with atmospheric CO2. So running an air stone during the lights on period could increase CO2 by bringing it up to equilibrium with atmospheric CO2?

Either way I wouldn't run an air stone in my tank as it is in the living room and the noise would drive me and the rest of my family to distraction with the so called 'silent' air pumps.


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## Gfish (22 Oct 2010)

First of all sod that, they can just turn the telly up if they don't like the airpump noise lol 

Things are complex in this world of air and water aren't they. I will read your reply again to try get it straight in my mind but there's a definite advantage of the airpump, I'm just not sure I can fathom why. It doesn't really disturb the surface though, as it's a long bubble curtain that's swept by current from the internal and then circulated about the tank. Maybe this is a key point. I'm going to look at it again tonight to see how much the surface is moved at the rear. But yes, her tank is stunning, one plant has been in there for years, and the tank and contents were given to us. With minimal care this plant is now huge! And I've added a few more so the tank looks very well planted with anubias, fern, crypt and bacopa. I'm not even sure what the big plant is lol 

Also, what's notable about this tank is I have the lights on for over 13 hours! Not overly lit but not a dim tank either.

Cheers

Gavin


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## dw1305 (25 Oct 2010)

Hi all,
The CO2 content of the water is only relevant when the plants are photosynthesising, at night CO2 levels will creep up as all the bioload is respiring and the plants are net producers of CO2, rather than net consumers.

I'm also not sure that the long phtotoperiod makes any difference in low tech set ups. I've often had the glasshouse grow-lights (400W SON-T) on a 16 hour day, this is fine in low nutrient set ups (although members of this forum who run nutrient richer wil tell you it a recipe for disaster high tech).

We used to have some big, planted, trickle filters in the landfill leachate lab. which are very efficient for gas exchange and these promoted very good plant growth, both emersed and immersed. I think you situation may be similar.

cheers Darrel


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## ceg4048 (26 Oct 2010)

Gfish said:
			
		

> Hi,
> I'm aware that having too much surface agitation in a Co2 injected tank is bad and understand the reason, but on a low tech tank is there an advantage to having an airstone, Venturi or excessive surface agitation? I.e over oxygenating.
> The reason I ask this is, of the 3 tanks in my house, my daughters 2ft is the healthiest by far. No signs of algae. A bubble curtain along the back wall. Masses of plants some very slow but others fast enough to need a trim every few weeks. And it's never been treated to more than the occasional pour in fertiliser and a weekly 40% water change or so.


Gavin,
     It's not really a good practice to link any one factor, like the airstone bubbles, to the tank's performance, or to compare the performance of multiple tanks - unless there is a specifically controlled comparison.

People are always doing this, even those who know better. You have to analyze tank performance holistically. What I mean by that is that there are so many variables. Not only are there many variables, but there are many degrees to the magnitude of those variables. All the effects of these variable add up to produce the performance we observe.

There is no way, given the lack of data about the tanks, that anyone can say with any certainty, what variables are responsible for what aspect of the performance. It's easy to draw illogical conclusions without any data whatsoever. Brainstorming possibilities for your reported observations cannot compensate for lack of precision or for lack of data.

Lets examine your statement for a second;
You have 3 tanks and one tank outperforms the other two. We have to assume that all three are planted tanks and that at least one of them is a non-CO2, non-Excel tank - but what are the other two? We know that flow/distribution makes a difference and that the larger the tank the more critical flow is. Are there differences in the sizes and is flow optimized in all three cases? Are the PAR vales similar across the tanks? Are the same plant species present across all three tank? Are the stocking levels high and are they more or less equivalent?

Is performance being defined in terms of the growth rates or in terms of algal biomass, or in terms of appearance or some combination of these metrics?

Unless we have solid data regarding these factors I just don't think it's a good comparison. Unless we have control of the metrics or control of the the application of nutrient/CO2 then all we really have is visual evidence of one tanks adaptability to it's particular set of environmental challenges versus the ability of another tank to adapt to it's unique set of environmental challenges. Without the ability to measure and control the environments then the comparisons are strictly random.

The same can be said of the claim that the dangers of high energy lighting might be an overstatement. What are the PAR values? What are the conditions of the tank? What are the actual water/sediment nutrient content? How long have the plants had to adapt? What are the species in the tank? Are there floating plants that limit PAR penetration? 

Steady state environmental conditions enable aquatic plants to make specific adaptations,
so it could easily be that one tank has stable conditions while the other two are unstable. Even if were such that the bubbles in this tank outgas CO2, the CO2 concentration could be stable enough during the photoperiod. Given time, the plants can adapt to very low CO2 levels as long as PAR values are not too high. About 50% of species have the ability to use bicarbonate. This function is immediately available under low CO2 availability. There is no waiting. Hydrogen ions are pumped into the water column which then shifts the equilibrium equation to the left and produces CO2 which is taken up straight away. Assuming a non-zero bicarbonate level, and assuming that a percentage of the plants have this ability then the high Rubisco efficiency plus the possible HCO3 conversion could be sufficient to keep the growth rates at a good clip. Nutrient content of the tap plus organic waste plus CO2 expelled by fish can be sufficient in a stable low PAR environment. 

There are plenty of examples of thriving low tech tanks so this shouldn't be surprising. If the other tanks are not doing as well as expected, then it speaks to the techniques being implemented in those tanks, which should be addressed on their own terms, not by comparing their relative performances.

Cheers,


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## Gfish (26 Oct 2010)

Clive,
I'll come back to you when I've written a book on each tank 
Mate, I only asked to see what other folk thought, everything you said is correct but the significance of the air curtain was what I was curious about. If it has no bearing on this tanks performance then ok, but i/we don't all have time to experiment enough with our tank/s to evaluate what is or is not significant, it takes many years i imagine, hence firing ideas and queries to eachother on these forums. 
You're addressing  the level of my technique of putting my point across rather than being constructive. Come on mate, youre better than that


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## roadmaster (27 Oct 2010)

Gfish said:
			
		

> Clive,
> I'll come back to you when I've written a book on each tank
> Mate, I only asked to see what other folk thought, everything you said is correct but the significance of the air curtain was what I was curious about. If it has no bearing on this tanks performance then ok, but i/we don't all have time to experiment enough with our tank/s to evaluate what is or is not significant, it takes many years i imagine, hence firing ideas and queries to eachother on these forums.
> You're addressing  the level of my technique of putting my point across rather than being constructive. Come on mate, youre better than that





Hmm, I am reminded of those who frequently post with concerns with sick fish. They often don't or won't take the time to answer a few questions regarding the enviornment the fishes are being kept in, and they want opinions on medications to use that will cure the fish immediately  .Numerous opinions are often quickly forthcoming and slews of different meds are recommended. What is gained by this?
I thought Clive made  a sincere effort to enlighten one to the possibilities that should be considered.
Not all, are so inclined.


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## Gfish (27 Oct 2010)

Ok thanks. Clive no offence was intended, and as in the past, your expertise is much appreciated, but it was a topic of conversation before that lengthy post instructing me of what I omitted and telling me all the information I'd need to give and take into account.
Not all threads need be so serious, my fish were not all dying, and I personally enjoy hearing of other folks findings with their own tanks. 
I may be wrong, but all I often try to do is keep it light hearted. It's a hobby remember.
I'm sure Clive ain't phased and possibly chuckled a little at my response. I hope so anyway.
Cheers
Gavin


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## Jaap (22 Jan 2016)

Gfish said:


> I'm aware that having too much surface agitation in a Co2 injected tank is bad and understand the reason, but on a low tech tank is there an advantage to having an airstone, Venturi or excessive surface agitation? I.e over oxygenating.



So do we have an answer to this question?


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## AndyMcD (23 Jan 2016)

Jaap, please take a look at photorespiration. 

This effect occurs if there is an excess of oxygen or insufficient CO2 (possibly in the presence of excessive light). It results in the plant releasing more CO2 and ammonia, which it tries to re-absorb (meaning it may absorb less from the water column), but needs to use its energy stores to do this.

https://en.m.wikipedia.org/wiki/Photorespiration

This effect may be irrelevant. However, it strikes me that it has a good fit:
- Occurs when insufficient CO2 for amount of light
- Occurs when excessive O2 and photosynthesising (switch airstone on at night)
- Means plants absorb less ammonia. Ammonia spike for algae?
- Plants need to use their energy stores to re-absorb CO2 and ammonia. Over time plants become less healthy


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## Jaap (23 Jan 2016)

AndyMcD said:


> Jaap, please take a look at photorespiration.
> 
> This effect occurs if there is an excess of oxygen or insufficient CO2 (possibly in the presence of excessive light). It results in the plant releasing more CO2 and ammonia, which it tries to re-absorb (meaning it may absorb less from the water column), but needs to use its energy stores to do this.
> 
> ...


So is it better to have an airstone or surface rippling?


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## AndyMcD (23 Jan 2016)

Jaap, honestly I don't know. 

Both will help gas exchange at the surface of the water, so will help you to reach the maximum based upon atmospheric levels (proportions in air O2 = 21% and CO2 = 0.04%). Obviously, only a very small proportion of these gases will remain in the water. 

I think Henry's law is relevant here. Cooler water holds more gas than warmer water.

The more you break the surface, the more quickly you attain the equilibrium levels. 

I guess you have the same issues dissolving the gases as you would dissolving CO2. I think an airstone works by breaking the surface rather than the bubbles dissolving in the water.

If you have a spray bar, you could point almost horizontal at the surface and I wonder if you would achieve a similar effect.

Obviously, excessive light could be an issue as CO2 low (and possibly O2 high).

Hope this helps.


Sent from my iPhone using Tapatalk


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