CO2 and fish
In my experience co2 at recommended 1/1.1 ph drop stresses fish. Have calibrated ph controllers and observe fish are less active when co2 is on then when co2 tanks empty or during off hours.
Gone to low high tech with bmled dutch xb light dimmers set to 0 from 15%, co2 ph drop to 0.9, and established low light plants. Fish are active.