Sorry , but I think you'd need to use a closeup or macro image to give a better idea of the problem. I don't have the best eyesight , so maybe I'm missing something most folks could see in the picture?

Hi, I have the same problem, if you find out what is causing this and what to do to correct it please e-mail me. Need help too.chandler_37303@msn.com

phosphate get a phosphate remover or just try cutting down on the light. ( if you have your lights on 10hrs a day try 6hrs) this will also help