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CO2/pH level in planted tank

Simanas said:
Tom,
How did you fix client's tank?
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Increased circulation and surface movement. This waste some CO2, but adds much needed O2.
See the differences in my 2 graphs for the lethal threshold?
The O2 is a good 2 ppm lower

Which is about 30% less O2.
I removed the cheap junky regulator, added a nice dual stage and nice needle valve etc.
Removed the canister filter, and added a wet dry and a post large canister micron filter.

Surface scum can cause havoc, as can changes in the KH if you use pH controllers.
I'm not much of a fan of canister filters.
 
tubamanandy said:
Ok, currently my 56 litre tank (KH 5.5) sits at PH 7.34, when lights come on & CO2 (gas) is fed into the reactor, PH only drops to around 7.21 slowly over the next 7 hours with addition of around 1 bubble/second.

With a KH of 5.5 I guess I would need to be adding alot of CO2 to get the PH below 7.0 ?

Thinking of dropping the KH to around 3-4 so I can get PH a little lower - am I making sense ?
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I'd add enough CO2 to get a pH of 6.6 or thereabouts and keeps it there after about 1 hour or less after the lights come on. If it drifts 0.1 pH units, you are okay, more than 0.2 ppm, some changes likely need to be made.

This assumes 100% of the KH is from carbonates
 
ardjuna said:
CO2 with strong aeration:
1110301bpsviolentaerati.png

On the other hand, Tom Barr (plantbrain) doesn't use aeration in his tanks, but uses wet-dry filters (which could play a similar role as aeration). That's the reason I asked him what is the reason of his constant/stable CO2 level throughout the photoperiod.

Maybe it could help a lot, if we have the CO2 on for 24/7. That way it could build up to the highest level, and stay there for 24/7. But in this case we need to add smaller amount of CO2, because there will be practically no degassing at night (or due to aeration), and therefore no rest for fish.

What do you think about it?
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This graph above is much more similar to what I typically have and find for my tanks. You 'll note the exponential increase that then starts to level off between 9 am till about 11 am, then stays flat. Lights and plant uptake has virtually NO EFFECT. This is because only 1-2% of the CO2 we add actually is delivered to the plant's carbon demand.
At first this may seem wasteful, but the counter point to all this is stability and ..........good O2 levels.

Good O2 cannot be overlooked in this. Since fish typically limit the upper bounds, and we do NOT need, nor should add CO2 at night, O2 must be addressed.measured in conjunction with CO2. The stability we are after is ONLY during the light period, there;'s no need to gas the fish chronically 24/7, we only add CO2 for about 8 hours and then the plants also are adding 1-2 ppm or more O2 as well.

With a wet/dry filter, the drop after you shut off the CO2 is very rapid, about 30-60 minutes, it'll drop to 2-3 ppm, with canister filters, it would only get down to 10-20 ppm for the 180 Gallon tank I had for an upper range in the 60 ppm's.
The O2 was in the 5-6 ppm ranges.

This was unacceptable to me so I switched to a wet/dry.

Wet/drys add their own issues, some can degas the system TOO MUCH. You need to find a balance that works.
Sometimes piling on more and more current is worse.
I prefer the bean animal style over flow(biggest issue for many is the prefilter section and then the dry section needs sealed up). It's very quiet and saves CO2 well, but still added plenty of O2.
 
plantbrain said:
With a wet/dry filter, the drop after you shut off the CO2 is very rapid, about 30-60 minutes, it'll drop to 2-3 ppm, with canister filters, it would only get down to 10-20 ppm for the 180 Gallon tank I had for an upper range in the 60 ppm's.
The O2 was in the 5-6 ppm ranges.
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Strange, but I dont get such a rapid degassing with my wet/dry... 2 hours after co2 shuts off PH increases from 6.4 to 6.8, when the PH in the morning is 7.3. Dry sections is not sealed, only the overflow is silenced from all the gurgling and splashing.
Question: does PH drop/increase instantly as CO2 change or is there some delay?
 
If anyone is interested in the charts of how CO2 concentration changes during 24h period in planted tanks, I put on my website some charts => see prirodni-akvarium.cz (it's in Czech language, but you can use Google translate). Technically these charts are not CO2 level, but pH levels converted into CO2 based on known KH. So it could be that these numbers are not as precise, but still we can have an idea of what's going on in our tanks. I use canister filters in all my tanks, and as I have found it is fully possible to completely degass CO2 ... if you use strong aeration and/or surface rippling. So the main key in CO2 degassing and in keeping stable levels of CO2 is aeration. When you don't use aeration or water surface rippling, then your CO2 will be contiually increasing until it reaches some maximum level. With 1 bps in my 60L tank the CO2 level was continually increasing from 11 mg/L (before lights on) to 80 mg/L (before lights off) => this is the first chart on my website. Now I know why my shrimps did not do well in these conditions. If I increased CO2 amount to 4 bps, and at the same time used strong aeration + surface rippling, then my CO2 level very quickly reached its maximum level of 35 mg/L (in just 2 hours), and then stayed there for the rest of photoperiod (due to constant degassing caused by aeration). I tried to lower CO2 amount to 2 bps also (chart #3) with the same result as chart #2 (only the CO2 level was a little lower => at 25 mg/L). Also some people supply the CO2 for 24/7 (without turning it off at night), so I simulated this situation also (chart #4). The key here is to use low CO2 amount (I used 0.5 bps), so that it doesn't accumulate too much. The drawback of this non-stop CO2 supply is that the CO2 level is increasing really slowly (it takes nearly 24 hours for it to reach the maximum level => in my case: 15 mg/L). The problem here could be also scum on the water surface. When it creates on the water surface, the CO2 level will quickly fall down. The last chart on my website (chart #5) is the CO2 level in planted tank where there is no CO2 supply, no aeration, just moderate surface rippling. In this case CO2 level stays constant at 4 mg/L. I'm doing some other measurements as to find out what has greater impact on CO2 degassing => aeration or surface rippling? Also keep in mind that I did these tests in relatively small tanks (60L), so the aeration and/or surface rippling in larger tanks may have smaller impact on CO2 degassing.
 
zanguli-ya-zamba said:
I wanted to know, why do say that with scum on the surface CO2 will quickly fall down ? I don't understand why ?
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I don't know either. It's the result of my measuments. But to have some serious data, I need to do more experiments.
 
really good thread

ardjuna - good work too!

I don't know much about fish biology so what is the mechanism that increases fish + inverts tolerance to co2 as o2 levels increase? Can fish regulate the osmotic pressures of each gas independantly?
 
Hi all,
bridgey_c said:
I don't know much about fish biology so what is the mechanism that increases fish + inverts tolerance to co2 as o2 levels increase? Can fish regulate the osmotic pressures of each gas independantly?
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It depends upon the fish, what species they are, and how big they are. It is dependent upon the "Bohr-Root" effect <Fish Respiration>. As a general rule fish from cool, fast flowing, highly oxygenated water (Hill stream Loaches (Sewellia lineolata etc., some "L." numbers (Chaetostoma spp, Pseudolithoxus spp. etc., Salmonids) are most at risk from high CO2, and for the same species large fish are more at risk than small fish (due to the differences in the body volume (^3) to gill area (~^2) ratio). From the Ichthyology link
...Suppose conditions deteriorate in the pond. Decomposition uses up much of the oxygen, producing abnormally high carbon dioxide levels.
  • Fish with a strong Bohr effect are in triple jeopardy:
  • There is less oxygen to start with.
  • They can't load as much in the blood because they have to load on the low curve.
  • They can't unload as much to the tissues since they will be unloading on the same curve they loaded on.
  • Fish such as carp and bullheads that often live in habitats that may experience such conditions, usually show relatively small Bohr and no Root effects...
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Cheers Darrel
 
thanks for the link.

So the only variable in the rate of diffusion of a gas is the difference in partial pressure between the two solutions, which is what I would have thought.

How then can fish tolerate higher levels of co2 dependant on higher levels of o2? Given that they cannot alter the diffusion rate of co2 into their bloodstream (unless they reduce the gill area) a higher co2 level in the water will always produce higher levels of co2 into their bloodstream. Tom's lethal threshold is dramatically increased by higher levels of o2. How so?
 
Hi all,
bridgey_c said:
How then can fish tolerate higher levels of co2 dependant on higher levels of o2? Given that they cannot alter the diffusion rate of co2 into their bloodstream (unless they reduce the gill area) a higher co2 level in the water will always produce higher levels of co2 into their bloodstream. Tom's lethal threshold is dramatically increased by higher levels of o2. How so?
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That is an interesting question, there is a thread on Apistogramma forums (that is worth a read for all sorts of reasons <ok | Apistogramma.com>), which covers this question. The consensus was that high O2 shouldn't make CO2 any less lethal, but Tom has found out that it does, so there is definitely something else going on. I don't have any animal physiology background, but the must be some-one who has an answer.

cheers Darrel
 
good read.

I think jaafaman in the last post has it right (not that I know much though!)

Maybe this is the process. Higher levels of o2 require less movement of water over the gills to provide enough o2 to satisfy respiratory demands. Therefore lower levels of co2 enter at the same time. If o2 levels are low the fish will need to pass more water over the gills (breathe faster) and thereby must increase co2 levels in the bloodstream at the same time. If o2 levels are low and co2 levels are high then this is the real killer. The fish will need to breathe heavily to satisfy oxygen demand and have no option but to absorb high (toxic) levels of co2 at the same time.

This would also explain why fish act more docile and hide when I inject too much co2, they are in fact trying to slow down their consumption of oxygen so they need not pass as large a quantity of water over their gillls which would absorb too much co2 at the same time as satisfying their oxygen demand. Maybe I need to rethink my tanks!! More surface movement if you want healthy animals....
 
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