Join Date: Oct 2006
Location: Leesburg Virginia
Having more CO2, even at the lower light duration, will allow the plants to better utilize the light that is available. My bubble rate is uncountable on a 57 gallon tank and the total light duration is 8 hours. I run one T5HO bulb for 5.5 hours, 3 bulbs for 1.5 hours, followed by the one bulb for the final hour. It has the least amount of algae I've ever had. In my case, it probably took longer than expected to build up sufficient CO2 to fend off the dreaded BBA.
Anyway, I went away for 4 days and I kept everything set the same except, not turning on the two bulbs for the 1.5 hours. I wanted to slow things down just in case the lower water levels from evaporation and the increased surface movement would off gas too much CO2. I expected less plant growth. Well, the Ludwigia didn't slow down and Sagittaria grew taller than usual. Probably wanting to grow closer to the weaker light. The plants were just as healthy and no string algae.
I would say keep CO2 high, its cheap. and your plants can still utilize the lower light duration and or intensity.