Here is something I read out of a book
How to Adjust Phosphate
The best way to limit phosphates in the aquarium is to restrict the amount of phosphates that get into the system to begin with. Since tap water can be a major source of phosphate, I warn aquarist not to use it.
RODI water are far better choices. Many hobbysists purify their tap water with both RO and DI prior to using it in their aquariums. This insures a minimum of impurities left in the water.
OTHER WAYS TO REDUCE PHOSPHATES
Use additives declared "phosphate free" on the label.
avoid over feeding
Use phosphate sponges or phosphate resins in the filtration system. Two common forms are white aluminum-based beads represented by products such as phosguard, phosSorb and the like, and a reddish granular powder that is a ferric hydroxide compound sold under names such as rowaphos. Fiber pads such as Poly-Filter and HSH Phosphate Reducer will also extract phosphates from saltwater.
If your phosphate levels are dangerously high, perform a 20% water change each day using purified water and phosphate free salt mix until the levels are reduced