I have used CHEMI Clean (should be available at your local pet store that carries SW stuff). It is about $15 and you get a very small amount (enough for two maybe three treatments). However if your tank is established, you need to find out what caused it to start with. Test all parameters of the tank including phosphate and nitrites/nitrates. If any of the above are high, are you using RO/DI water? If you are, then get some culpera plants (supper cheap and absorb the same ingrediants that nusance algae uses and looks much better. Chemi Clean works pretty good.