Water flow vs CO2 solubility
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Old 06-07-2014, 08:51 PM   #1
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Water flow vs CO2 solubility


So this is more of a chemistry question. When I increase the water flow with my filter, I see that there is less O2 pearling. I think (correct me if I'm wrong) this is because increased liquid solvent movement increases it's saturation point allowing more solutes to be solved creating a slightly supersaturated solution. At the same time increased flow rate increases gaseous exchange at the surface due to increased surface area. the current flow rate in my tank is not strong, but my tank is so small that even a slight rate agitates all water content in the tank easily. I have been looking at my fish and they are acting completely normal, swimming in the lower depth of the tank. So, my question is: Are the plants photosynthesising as a higher rate with increased water flow? or is it just the same?

Thanks for your help
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Old 06-07-2014, 09:03 PM   #2
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I can see a couple of things going on, not sure which is the answer. Probably a combination.

1) The water RIGHT next to the leaf is still. Just a molecule or so deep in average water movement situation. Several molecules deep in calm water.
More water movement may rub the leaves against each other, and can be more actively bumping into that 1-2 molecule layer next to the leaf. This allows other molecules to get next to the leaf.
What this is doing is... a) Knocking off the oxygen molecules before they get big enough to form a large bubble. and b) Allowing the CO2 to get next to the leaf so it might get taken in more efficiently. In this sense I think that more water movement is better, up to a point.

2) More water movement does indeed create more surface movement which will allow more gas exchange. When you are adding CO2 to the water you are losing more at the surface. If you are not adding CO2 then the water gains CO2 with surface activity. Some water movement does beneficial things like breaking up surface scum, so I would not want a zero water movement tank, but it is not necessary to have a lot of water movement.

3) Too much water movement can harm the leaves, so there is some balance there between too much and not enough water movement.

4) Fish behaving normally is a good sign.
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