High phosphate

[Dom]

I thought water changes do nothing in bringing down phosphates?

Why would water changes work for bringing down Nitrates and not Phosphates? Both are present in the water and both are removed when siphoning out water for a water change.

 

[ReefGeezer]

I thought water changes do nothing in bringing down phosphates?

A 20% water change reduces phosphate by 20%. But leaching from bound phosphate in rocks will quickly raise it right back to the original level. It is hard to imagine that you could reach your goal doing weekly 20% water changes. To reduce phosphates in the 1 ppm area, including that bound in the rocks, I'd use Lanthanum Chloride to get in the .05 ppm range then use a fuge or GFO to keep it there.