# air stone



## Diana (Jan 14, 2010)

Here are the sources of CO2 in a Walstad tank:

Air exchange. When water with low CO2 is in contact with air it will pick up more CO2. The question is: how much CO2 is in the water? It is a benefit to increase the water circulation? If there is already a reasonable supply of CO2 in the water, then circulating the water can allow the CO2 to leave the water. 

Organic matter decomposing. This is a low level, but is suited to the level of other nutrients in this sort of set up. 
Fish respiration. 

If the sources do not supply very much CO2, then the plants will use up this supply, and additional water circulation will bring in more. 
If the sources supply more CO2, then it will be enough for the plants, but more water circulation can drive it off. 

Without some tests it is impossible to say which way it will go. 
You could get a drop checker. As it changes color through the day you can figure out which way brings in the most CO2. 

Some water circulation is important. This will bring whatever CO2 there is in contact with the leaves, as well as nutrients from the decomposing materials. Generally, a light ripple at the surface is about right.


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## masoudj021 (Nov 18, 2015)

Diana said:


> Here are the sources of CO2 in a Walstad tank:
> 
> Air exchange. When water with low CO2 is in contact with air it will pick up more CO2. The question is: how much CO2 is in the water? It is a benefit to increase the water circulation? If there is already a reasonable supply of CO2 in the water, then circulating the water can allow the CO2 to leave the water.
> 
> ...


 thank you for the answer
my only CO2 source is breathing of fishes . about 20 fish( rainbows) in 40 gal somehow heavily planted tank (somehow the same as Diana Walstad's tank if I'm right) . I'm planning to use siesta lighting method. So what's your opinion? Can this air stone help or it's harmful for my little amount of CO2?


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## Diana (Jan 14, 2010)

I have no way of knowing. 
CO2 alters the pH of the water. You can test the water for pH through the day, and follow the changes. This could help you figure out if there is enough CO2.


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## Eutexian (Mar 11, 2015)

I see no mention here of one small fact of plant ecology.

when they cease photosynthesis.. the plants begin to produce co2, or rather it increases.

so.. when the lights go out.. co2 levels begin to climb. This is why Walstad herself recommends a middle of the day 'siesta period'. and in her book provides a graph showing how the levels of co2 rapidly fall in the morning from an overnight high.. and then during the siesta rise again.

as below.

over a 14hr period.. 5 (lights on) 4 (lights off) 5 (lights on) then off for 10 hours overnight.











below is the actual graph in her book p179 comparing the siesta with continuous light.










I dont use an airstone in any of my tanks.. its completely unnecessary if the tank has at least some movement from a pump or filter outlet.


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