Originally Posted by vqfive
Plants release co2 and consume oxygen at night when lights are off. So in the morning your water would already have a high level of co2. Turning on your co2 an hour before lights come on is just wasting co2.
True and maybe as there are many other considerations that affect the co2 start timing. For example, I am running pressurized co2 in a high-light over-planted and over-populated tank. In that tank I also run a bubble wand when the co2 and the lights are off to protect the fish. When the lights come on, the concentration of co2 in the water is around the equilibrium with co2's concentration in the air, which is pretty low for plants in a high-light aquarium.
Other variables are the surface agitation, the method of the co2 injection, the co2 delivery start-up time, co2 distribution within the tank (flow), and who knows what else.
My point being that, unfortunately, one size does not always fit all.