Re: Will a digital pH meter read accurately at high chlorine
Note that the pH does rise when you add a hypochlorite source of chlorine. How much it rises depends on the initial pH, the TA level, whether there is CYA in the water, and whether there are borates. The following gives the pH rise for different scenarios when adding 10 and 20 ppm FC:
80 ppm TA, 0 ppm CYA
adding 10 ppm FC
pH 7.2 to 7.43
pH 7.5 to 7.76
pH 7.8 to 8.03
adding 20 ppm FC
pH 7.2 to 7.62
pH 7.5 to 7.93
pH 7.8 to 8.16
80 ppm TA, 30 ppm CYA
adding 10 ppm FC
pH 7.2 to 7.52
pH 7.5 to 8.13
pH 7.8 to 8.48
adding 20 ppm FC
pH 7.2 to 8.08
pH 7.5 to 8.54
pH 7.8 to 8.74
80 ppm TA, 30 ppm CYA, 50 ppm Borates
adding 10 ppm FC
pH 7.2 to 7.41
pH 7.5 to 7.73
pH 7.8 to 7.98
adding 20 ppm FC
pH 7.2 to 7.65
pH 7.5 to 7.91
pH 7.8 to 8.11
So you can see that 50 ppm Borates pretty much counteracts the extra pH rise associated with having CYA in the water. CYA causes the pH to move more when you add chlorine because CYA is a hypochlorous acid buffer so when hypochlorite is added, most of it becomes hypochlorous acid that binds to CYA whereas without CYA much more of the hypochlorite remains so.