How to conduct daily PH test when FC level is above 10 (not during SLAM)

[mazhiqiang69]

Hello
According to the Table, based on the CYA level, we should keep the pool's target FC at a certain level accordingly. What happens if the target FC level is over 10? Because I also learn that PH test is not valid if FC is in double digits. Does it mean if I need to keep my daily FC at 12 (CYA-100, not during SLAM), I can't conduct any more PH test?

Thank you!

Kevin

 

[JoyfulNoise]

Two choices-

1. Let your FC drop to 10ppm and measure, then raise it back up.

2. Take your water sample for pH testing and dilute it 1:1 with distilled water (you could even do 2 parts pool water to 1 part distilled water). It has to be DISTILLED WATER (the kind you buy in the supermarket for use in irons and coffee pots). The pH of the pool water will be (mostly) unaffected by dilution because the alkalinity will buffer the pH change. Distilled water has a pH of ~7.0 and very little alkalinity (typically <10ppm). Dilution will cut the FC down by half, so you can test pH.

Also, at 12ppm FC you can still get a decent pH reading, you just have to do it quickly. The chlorine neutralizers built into the R-0004 phenol red reagent will neutralize up to 10ppm FC. However, near 10ppm FC, the reaction of chlorine with phenol red is typically slow enough to allow for a person to read the pH before the purple interference builds up. The test definitely fails above 20ppm because the reaction is too fast at that point.

Bottom line, even at 12ppm FC you can still get a decent read of your pH.

 

[mazhiqiang69]

Sounds good, I will do it, thanks!

BTW, in a long term, I think I will replace current pool water by some fresh water, and ultimately reducing CYA to around 50 (now it is 100), then I will have a low target FC and can test PH without any restrictions.