Soil has low PH

I'm 2 weeks from harvest and have started noticing a P deficiency I tested the ph of my run off and it read 5.4 coming out. I suspect low soil ph is my problem and is causing a P lockout. Since I am 2 weeks from harvest I'm 5 days into flushing. Should I just continue to flush or should i try to fix before harvest? Also how do i raise the ph in my soil? I flushed today with non phd tap water at 7.2 ph will watering with a high ph bring the soil ph up?

Also I've been using general hydroponics trio for nutes with calman and floranector and always used ph up or down to get ph between 6.0 and 6.5 before watering. Could this be why my soil ph is low? Does the ph down that I use build up in soil?

Soil runoff doesn't tell you anything.

Thats only for coco and hydro.

Focus on the pH of what's going in not whats coming out.