Your phosphate level could be high try looking into a phosphate reactor, sum people have two reactors each with two different media, one with carbon, and the othe with phosban. Try not to over feed, fan your rocks and sand with your fingers, and dont leave your lights on for more then 8hrs, if u have to cut the time, and raise your light fixture so that is not to close to the water, and make sure you replace your bulbs every 6 months. I'm having an algea issue to, and just learned it was my phosphate. Basically what im telling you is what im doing myself... good luck