ph reading changes to higher reading within a minute or two

[vtdhc]

My son is trying to get his above ground pool (about 19,000 gallon) cleared up after the winter. He just had it in shock mode for a few days and the water is looking much better compared to the "swamp" he had last week. The water is still somewhat cloudy but last night he passed the OCLT test with only 1ppm FC loss. Last week his ph reading was off the chart high but today the reading started at about 7.3 and fairly quickly changes higher to about 7.6. I wish I had testing his FC level but didn't because it was pouring rain. I suspect it may be on the high side since he was in shock mode until yesterday. Last week when we started his test levels were.....
FC = 0.0
PH = 8.4
TA = 60
CYA = 25
CH = ? didn't test

So what I'm wondering is what might cause the ph reading to change from 7.3 to 7.6 within a minute or two? Which reading should we believe ? How to best clear up the cloudy water ? It's not real bad but you can't see the pool bottom and as I said it's an above ground pool.

Thanks, Dave.

 

[spinPHD]

If he is in the middle of a SLAM, I'm assuming his current FC level is above 10. If it's above 10 the PH test is inaccurate, so you can't trust either. Either way, if it is 7.3 or 7.6 those are both acceptable levels so shouldn't be a problem. Just needs to keep SLAMing, by using liquid chlorine or bleach only.

 

[jblizzle]

Likely the FC is above 10ppm and that is skewing the pH test.

IIRC, it may actually read correctly right away ... so I would guess they are around 7.3 and that the FC is not too much above 10ppm since the change was slow.