by the way thanks man i'm goin through the same thing and didnt have to ask anyone because this thread gave such good info... just thought i'd say thanks to the guys that answered you
Actually if you reduce your macros you stress your plants and the algae will grow more. Adding CO2 would actually help the most since it helps the plants grow faster and out compete the algae for nutrients.
i would only leave the lights on for 10 hours max a day. i would have said throw some inverts in there but it doesnt look like an option for you. R/O water works well too