phosphorus deficiency,what to get.

here's whats up:looked at the plant problem guide up top.found out that it's a phosphorus deficiency,got some soil test kit's for n,p,k test so i know 100% it is and soil ph is fine. Question is i don't know what product to get at lowes etc,or hydroponic store.Other question is i just fed it big bloom 1day ago so when would i apply the product?
id really appreciate fast input so i can fix this today or soon as possible,thanks