CO2 and fish health / respiration?
I have a high tech setup, 50g tank and I've been running 30ppm CO2 based on pH and drop checker.
In that month, plant growth has been excellent, but I have some keyhole cichlids (only fish in tank) and noticed that their respiration is generally faster. Noticable gill movement.
The past two days, I disconnected the CO2 to get it refilled, but local Dick's needs a repair to their fill station, so I have a very short photoperiod while I wait for a refill. Without CO2, fish respiration is back to normal, and one of the pairs spawned!
This leads me to believe there is not enough oxygen in the tank. I have a large airstone running 24/7 and the return bar is angled up to ripple the surface. Nothing I have done while running CO2 has gotten the fish's respiration to slow.
Any suggestions? Could it be the are stressed by the rapid pH change each day? Is high tech generally not good for fish?