Are you adding CO2 and doing EI? I would definatly stop dosing KH2PO4 if you have tap water at 5ppm anyway, that will probably sort out your high figures. Are you adding K2SO4 as well? If you are you could increase the dose of that, (ask Tom for guidence on that one) to bring the potassium levels up.

Some fish foods do have phosphates in them, although I think theyre getting rarer. It should say on the side of the tub if it has/hasnt.

I wonder though that if your getting good stable growth and no algae problems then it might be worth leaving it be? Tom regularly says that high PO4 on its own hasnt shown to trigger algae blooms, its generally down to some other factor.