pH Testing

[bmgo]

Im confused about pH testing.
Do I add sodium thiosulfate to the sample or not?
There is a big difference in results depending on what I do.
Thanks

[ivyleager]

Some advocate adding sodium thiosulfate if chlorine is EXTREMELY high. However, with that said, it's never been noted here or elsewhere what that HIGH level would be.

My PS233 testkit pH instructions read: "If the chlorine level is above 15ppm wait till chlorine drops before testing."

Not very clear, I'll grant you that.

CaryB
Go 'Canes!

[waterbear]

The better pH reagents such as the one in Ben's kits and the Taylor reagents already contain a chlorine neutralizer in them at a level that won't have an appreciable effect on the pH. Adding extra could cause the pH reading to become higher than it really is. Some of the cheaper 4 and 5 way kits advice you to add a drop or two at high chlorine levels since their reagents do not contain a neutralizer. An extra drop or two with a reagent with the neutralizer in it might help you get a better idea of where your pH is but the reading is still going to be off.
If I am not mistaken both Ben's and Taylor's reagents will give accurate readings up to 15 ppm chlorine.