Please help-pH in rockwool too low

Growing in 6" rockwool, 6 weeks into flower in flood and drain. Every day I check pH in rockwool and it is around 5 (pH pen broke, so using drops). I up rez to about 6.5-7 to try and raise pH in rockwool each day. After flood rez is 6 and rockwool is 5.5-6, but the next day it's low in the rockwool again. Any ideas?

TIA,
RedEye

Are the plants looking healthy? If they do stop using ph up. VV

Agreed with VV (as usual). I'd stop correcting until you can get a new meter.

Colour-match pH kits may get you in the ballpark but it's harder to discern small changes (under 0.5 pH change) with colour match kits.

Well, my white widow doesn't look too good, and I am thinking the pH is the cause. I flushed them a couple of weeks ago and lowered ppm, but that didn't seem to help. Then I got the idea to check the pH inside the rockwool. Am I on the right track? Also, this close to harvest is there even any use in trying to correct the prob. or is it too late?

Damage to leaves doesn't heal. As long as the new growth is ok, you've probably fixed the problem. Time to get a new pH meter.

If rockwool has been flushed out well before use, it won't have much effect on the system pH. Residual limestone dust in rockwool from manufacturing can cause pH to jump up.

If rockwool is well flushed before use, the pH you measure in your tank is pretty much what the plant is seeing when exposed to the same solution in the rockwool.

I flush my cubes and soak them for a day before using them. However, I use rockwool floc (loose rockwool resembles bulk fibreglass insulation) in pots in my flood system. There's so much of the stuff in my op that it's just not practical to fully flush it nor soak it. I just run my tank pH a little lower than normal to compensate for the slightly alkaline rockwool floc, around 5.2-5.7.

If you only have a couple of weeks to go, I wouldn't muck around with it much. If in doubt, plain tapwater is a lot closer to right than a solution which has been corrected without good pH measurement tools.