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My planted tank maintains a CO2 level of 30+ ppm (using KH/pH method of calculation). The standard in the hobby nowadays seems to be 30 ppm, because some research suggests that 30ppm is all that the plants are able to use.

My question, then, is why do plants pearl/stream far more heavily after a water change for a few hours, even in a tank with 30+ ppm CO2? My tapwater is saturated with CO2. If 30 ppm is the maximum usable by plants, why do they seem to produce more O2 (implying more growth) at levels that exceed 30 ppm, even temporarily?
 

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A "pulse" can push the plants further, but only for a short peroid.

Other gases are also staurated above 100% in Tap water, especially if you use slightly cooler water(all gases are more soluble in colder water, thus cooler water holds more gas at equilibrium), they will off gas as well.
You might think it's all plant production, it's not.

I looked into this a lot about 9 years ago or so.
I knew i needed more CO2 so I added more and more till I got the results I liked. But after a a day or so, the growth backed off eve though I have plenty of NO3/K/PO4/traces etc.
So I tried amping the CO2 for the day to see.
It worked.

Before I came along and started bugging people about more CO2, it was 15ppm.

Chronic vs pulses makes a difference.
Tap water temp, concentration, test methods play some role here.

Regards,
Tom Barr
 

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My aquariums on the 6th floor get a water change which is charged with gas. The resevoir downstairs is pressurized with an air pump so that the head can reach 9 floors. (My other tanks are in a basement location nearby).

When I change the water in the 6th floor tank, it fizzes for about half a day. The plants, apprently pearl. I strongly suspect that the mass of bubbles is an out-gassing of the water and is not only a CO2 in O2 out photosynthetic process going on. I suspect that the texture of leaves aids in the formation of bubbles and the general outgassing of a supersaturated solution or CO2 and nitrogen. But I do not have the means by which to test this hypothesis.

Andrew Cribb
 
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