I had this issue a few years back when setting up a new tank. I hated the idea of using chemicals to treat the free floating algae, but I had tried everything (not turning lights on for 2 weeks, increasing filtration, adding an air stone)...so I could either buy a UV that could cost me $100+ or buy a $5 bottle of algae control (I bought Tetra Algae Control and it cleared my water up to sparkling clear within a few hours and I never had to use it again). My fish did not show any ill effects from the treatment. Just be sure to follow the instructions in regards to how much to use.