Please Help! pH Problems. +Rep For Any Help

So here's the deal... My girls on on their second day of flowering. This morning I fed them their nutes, the pH was 6.9. When I tested the run-off from the soil the pH was 5.5. Last time I fed them, I fed them a solution with a pH of 5.9. I didn't have pH up at the moment and they were very thirsty. This was like a week ago, and the pH was only too low that one time.

So why is my pH so low, any ideas? Is it going to cause problems? Right now they look very healthy. What should I do? Do I flush, start watering them with a high pH solution (like 8 or something), or do nothing and keep feeding them on their normal schedule with a pH of 6.5-6.8?

I really really appreciate any help, I love my girls I don't want them getting sick. So of course +Rep for any help. Thank you much RIU you guys and girls are the greatest.

Really nobody will help me out? Please.

if they look good dont stress about it if leaf curl or anything like that starts happening flush with straight water and it should bring your soil to neutral.

do you know what the ph of your plain water is

I use R.O. water. I think it has a pH of 6.8 or right around there. The water run-off from the soil used to be closer to 6.8, I don't know why it's so low all of a sudden.

i would not worry about run off. As long as you are holding at 6.8.

The run-off is 5.5. What I feed them is 6.8. So why does 10 min in the soil change the pH of the liquid go from 6.8 to 5.5. Don't need to stress about it you say?