I would expect using it 24/7 your co2 input would be much lower than 40 cc/min, all you would need is to match the off-gassing rate of your particular aquarium. At the very beginning of the 24/7 schedule you would need to inject something greater in order to overcome that off-gas balance. Once the target is achieved you would have to decrease the rate just to maintain it.
When I was manually dialing in CO2, I never changed the rate. Just a constant 40 cc/min.
My degassed pH was 6.40. Reading right before CO2 comes on was about 5.95 (does not fully degas overnight).
After two hours, pH was about 5.2 right when lights come on.
Slowly got lower then peaked at about 4.95 and stayed right there until CO2 is turned off. So in my 120G, it takes a steady flow of about 40 cc/min to maintain peak pH drop. I remember when Burr was running his 120G, his was even higher, more like 60 cc/min.
If I would dial back the flow during CO2 period, pH would predictably rise.
Now I do have a lot of surface agitation at all times. And I do run heavy aeration for 10 minutes an hour. This is really to make sure O2 is optimal for the Bows, and the heavier flow moves waste/detritus to the back edge of the tank.
Now the reason I know all this in such detail is I was dialing this in during the peak of the Pandemic. So was home a lot and carefully observed and noted everything that was going on. After carefully watching this cycle, I determined it was easier just to go back to the controller.
With the controller, I set the peak drop to 4.95. I run the flow meter at 50 cc/min, and the tank is almost at peak drop right when the lights come on. From there the pH bounces around from 4.95 to 5.05 all day long.
Still not seeing how one can possibly use less CO2 running 24/7.......but my ears are still open!
are you running CO2 24/7? Because if you are, based on your results lately might be worth a try!
Are there any issue with introducing animals straight into a 15-30PPM tank?
It's better to add livestock during a non CO2 portion of the day. If I am adding fish, I stop CO2 injection the day before and let the tank fully degas.
When you introduce a fish into a tank where pH is dropped by CO2, they can start gasping immediately. The smaller and younger the fish the worse it seems to be. I don't claim to know why, but I have seen it enough times to know that it should be avoided.
Funny thing is after being in the tank overnight, CO2 comes on next day and never seen a problem.
Again, don't know exactly why, but smart thing is to err on side of caution and get the tank fully degassed before introducing them.