You should be able to gradually work the phosphates down with GFO
, Phosguard or other phosphate binding products. Source of phosphates is generally; tap water, over feeding, fish died and wasn't removed, or some types of fresh live rock. Even as algae dies back it re-releases nitrates and phosphates. The ratio is as high as 16 parts nitrate to one part phosphate. So you have to continuously provide a fast binding agent to grab the phosphate before more algae is created. You end up starving the algae, but you can only go so far as your corals need some very small traces of phosphates to sustain its algae.
The only other long term solution I have found is using a ATS to use algae to starve out other algae.
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