Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I do not know if the organic choice is available. I see it at the miracle gro web site, but I have not seen it in local stores for several months.
CO2 dissolves in water, but only a certain amount.
Gases in the air above the water will dissolve in the water, but only in the top few molecules of the water.
Gases in the water can leave the water, but only when they are at the surface of the water.
If the water has too little CO2, (because the plants used it all) then the water at the surface will take in more CO2.
If the water has too much CO2 (fish respiration, or decomposing matter, or adding CO2 from pressurized or DIY system) then the water at the surface will release CO2.
Note, I keep specifying that this exchange of gases happens only at the surface.
Lets circulate the water.
Option 1) Tank water is low in CO2. Circulation will bring the enriched water from the surface to the lower areas, and bring the deficient water to the surface where it will gain CO2. Good to add air pump.
Option 2) Tank water that is rich in CO2. Circulation will bring the deficient water from the surface to the lower areas, and bring the CO2 rich water to the surface where it will lose CO2. Bad to add air pump.
Now the tricky part: Which is your tank?
If you are adding CO2 (Pressurized or DIY) then do not add an air pump.
If you are not adding CO2 (or if you use Excel) then the air pump MIGHT actually help bring more CO2 into the tank water by increasing the water circulation.
Here is a general guide:
In both sorts of tanks there is a lot of benefit to having a gentle ripple at the surface, and not much benefit with more water movement or less. Start with a gentle ripple.
Watch surface scum, plant growth and fish behavior to decide on more or less water movement.