Tom has always said he prefers to shut off the CO2 at night, to give the fish a break and to save CO2. When my solenoid valve failed and would not shut off I ran CO2 24 hrs a day for a month, and I saw no fish distress as a result. But, that may mean I was running too little CO2.
i had the co2 on a timer with the lights and im now running it 24/7 the tank looks great and the little algae i had is gone. BUT i also switched to pmdd premix and EI about the same time so im not sure if it was the co2 or i the change in dosing or a combination. It seems its working fine like it is but was looking for feedback.