I would have CO2
turn on 2 hours before the lights, and shut off when the lights shut off. This is always best done with a solenoid valve on a timer in sync with your lights on a timer.
Sorry to tell you, but 20oz of CO2
on a 55 gallon won't last you very long, a few weeks to a month max.
is dropping the pH of the tank water a full 1.0 – 1.2. To do this, measure the pH of tank water with no CO2
dissolved in it, and then measure again 2-3 hours after CO2
has been running. Ensure the drop in pH is a full 1.0-1.2. If the drop is not there yet, slowly up CO2
over a few weeks until at least a 1.0 drop is achieved, and watch fish / livestock carefully. Adjust CO2
down if you notice fish gasping at the surface and consider running an airstone at night when pushing a 1.2 or greater drop. For example, a tank water pH of 7.5 with no CO2
dissolved in it, should reach a pH of 6.5 – 6.3 for CO2
to really shine, and for maximum plant health.
Consistency in CO2
levels is key to plant health. Keep CO2
levels as stable as possible once a desirable level has been reached.