your temp is too high probably...68 is what to shoot for. make sure you have enough bubbles also. I have a similar problem, super thrive is great for algae growth also when the temps aren't right iv heard. H2O2 is a good fix but be aware it will kill some beneficial microbes as well. For initial application I use 30ml per gallon then around 1/4 that every day after. Your plants will tell you if its too much....