Planted Tank Obsessed
Join Date: Jan 2015
Location: Newmarket, Ontario, Canada
To confirm the 1.0 pH drop will reach CO2=30ppm, some quick math:
CO2 (ppm) = 3 x kH x 10 ^ (7-ph)
Assume a starting CO2 of 3ppm, and target CO2 of 30ppm, sets up two equations with two unknowns, and simplifies to:
10 * 10 ^ (7 - ph1) = 10 ^ (7 - ph2); where ph1 is starting ph, ph2 is target.
Take log of each side:
log10 + (7-ph1) = 7-ph2
and finally ph1 - ph2 = log10 = 1.0
If your starting CO2 level is 3.0ppm, then lowering the pH by 1.0 will give you CO2 of 30ppm. Notice that this is independent of kH. If you are dropping more than 1.0, then either you started less than CO2=3ppm, and/or you are achieving higher than 30ppm.
The kH does matter in terms of where your starting ph is (high kh = high starting pH, low kh = lower starting ph).
Evaluating the CO2 savings from turning off CO2 in the night;
The apex graph from andy gives a great illustration of the gas-off rate vs. the gas-in rate. I'd be curious how much surface agitation his system has. The amount of time the CO2 will stay on depends upon the gas-off rate. In his case, the gas-off rate is quite slow compared to the gas-in rate, so the controller would only kick in for a few hours/night (not bad). But if the gas-off rate was steeper, the CO2 would be on much longer in the night (not so good if you want to conserve gas).