Hey,
I'm not sure how long it will take, but if you're using tap water I think you're asking for trouble. RO/DI water is the way to go IMO. Even people who have been using treated tap water for years will suddenly have problems because the city they live in changed the way they treat the water. To move things along I would do a water change with RO water to get alot of those phosphates out of there.
HTH,
Dan'l