LIghts on or off, if you are suffering from an algae problem then you most likely have a nutrient problem, so what about the lights, unless they are of improper spectrum.
You need to attack the nutrient problem.
You need to find the spectrum of your lights or consider the age of the lights and them loosing their spectrum. What is your lighting?
Not sure what you are testing with but sometimes yo need to get nitrate and phosphate test kits with low end testing, because you could have trace nutrient problems.
Is there an active skimmer on your stystem?
Does any mechanical filtration need changeing?
Just a few thoughts.
Thomas