High CYA, so keep FC high, so are my high PH readings, falsely reading high ?

[tdurban]

Ben - you helped me last year understand why I could not keep my FC level up, and my PH level kept dropping. I had a CYA around 240, I was using Tri-chlor tablets which kept pushing my PH down. I switch to the BBB method and WOW what a difference. This spring when we opened the pool, it was the absolutely BEST opening we've had in it's 16 yr history !!! So Kudos to you and pool forum !!
Now this year my CYA is about 140, so I'm keeping my FC around 8-14. My PH seems to be reading close to 8.0. I've read where if you keep a FC above 10ppm that you will get a falsey high PH reading. So my question to you is, is that correct ? If so, should I only test my PH when below 10ppm ?
Thanks again, I can't tell you how much $$ we've saved this year and how sparkling our water looks, best ever !!

[chem geek]

The rule about the pH test falsely reading high when the FC is high is actually more of a problem when there is no CYA in the water. With CYA in the water (at usual FC/CYA ratios), the reaction of chlorine with the pH dye is slow enough that if you take your reading right away you should get a correct result. If you wait 30 seconds or a minute or more, then you may see the effect of chlorine reacting with the pH reagent to create a falsely high reading. The pH indicator dye reagent contains some chlorine neutralizers, but chlorine levels beyond that can react with the dye but with CYA in the water they do so over minutes, not seconds.

So your pH may indeed be at 8.0 since adding chlorine to raise the FC does raise the pH (it only drops back down when the FC drops back down). Unless you have metals in the water, having the pH be at 8.0 is not a problem, but your pH test may not read much higher than that so you are probably better off lowering the pH a touch down to 7.8 where it may still be reasonably stable.

[tdurban]

When you say 'since adding chlorine to raise the FC does raise the PH'...just to clarify, I'm using liquid chlorine, which I thought was PH neutral ??