Originally Posted by Dinogeorge
I agree with Bonita,
But would add that you should siphon off as much of it as possible and then do a water change using RO water if available. If not, plain water is ok. There are a number of reasons for this stuff, but the three things you can do to fight it are lights, phosphates and water movement. You want plenty of water movement in your tank, reduce your lights, as Bonita suggested, and reduce your phosphates. Flake food can be loaded with phosphates, so if your feeding it a lot, cut that back.
Good luck man.
Plain water as you suggest is NOT ok, it is often very high in phospates, which will make the problem worse. Keep your lights off for a few days, reduce feeding and do water changes with some RO/DI