One thing i figured out with the Pureblend Pro is that when i mix it the ph goes to about 4.5, but if i let it sit for a day it goes to 5.8 all by itself. Are you adding ph up at all? I also switch to pure blend pro soil, from pure blend pro hydro for the last 2 weeks of flower, cause its 1.5/4/5 vs 2.5/2/5