I know when I had GHA two different things worked the best for me. The first was getting a phosban reactor and using either phosguard or phosban to absorb and reduce the level of phosphate in the water. My preference, the phosguard seemed to work better for my tank. The other method, which people sometimes disagree with, is to use marine algaefix from API. If you use this, be sure to follow the directions to the letter. Like I said, some people don't like using this method because your putting chemicals into the water but again, it worked great for my tank and wouldn't hesitate using it again if needed. I never had any damage to the fish or coral from either method. If I had to choose between the two, I would pick the phosban reactor. Good luck.