pH not so stable after all - hTh kit

I have one of Ben's kits but have been using up supplies in an hTh 6-way test kit from Wal-Mart that I bought while waiting for the good one to arrive.

I tested 7.5 pH, as usual, but thought it a bit strange that it wasn't trending upward. Granted, it usually does so slowly, but my last muriatic addition was 2 cups back on 8/21 - and this gunite pool is just 3 months old - and I have an SWCG.

So, because my hTh reagent was getting low anyway, I broke out the one in Ben's kit and - WOW - my pH was close to the 8.2 level color, probably 8.0 :eek:

Being the skeptic that I am ;) , I redid the test with a different R-0014 phenol red from a Leslie's/Taylor kit that I purchased to be able to test FC (again, prior to the arrival of Ben's). That test also confirmed the high 8.0-8.2 pH.

I know the hTh kit worked for higher pH early in the season, as my initial pH was 8.2. The kit has been stored out of the sunlight in the kitchen.

I don't know if anyone else has/had this problem, but if your pH seems to be staying put just a little too long and you have an hTh kit, better get another kit or have your water tested at a trusted pool store as a double check on your reading. Now, I'm out to the pool to add some muriatic acid!!

This has been discussed somewhere else on the forum. Basically the HTH kit doesn't neutralize the chlorine in your pool before you run the test so the reagent doesn't turn the correct color at a given pH. I've got the HTH kit and another off brand kit. The generic kit tests much higher pH in my pool because it includes Sodium Thiosulfate that you add to the water to neutralize the chlorine before you test.