How long does it take for phosphates to go away?

ok si i started a 125 gallon reef on november 5th 2010 and im having a major phosphate problem. i got 120 pounds of sand new. im using ro di water and the tds meter reads 0. i got about 200 pounds of live rock and it was all from an established but neglected tank so i think thats whats causing the problem. how long will it take for it to completely go away because i have alot of algae and my corals are turning brown. but with proper care how long will it take to go away and will it also infect the sand and also theres no way im tearing down the system to cook the rock so please dont even suggest that.