You will never raise your mag with that method get bulk mag chloride and bulk mag sulphate from jl follow this recipe.
http://www.reefkeeping.com/issues/2006-02/rhf/
Pretty sure it's safe to raise mag by 100 ppm a day. This is a link for a reef calculator to figure out the amount to use.
http://reef.diesyst.com/chemcalc/chemcalc.html
As for phosphate highly doubt your method at use now will do anything you should be running a reactor with rowa or gfo even with a reactor it's gonna take a bit to remove phosphates now.