I started shocking my pool last night to try and once and for all get rid of some mustard algae. Before starting, I checked my pH using my k-2006 kit.

It was surprisingly high (> 8). Since I have been keeping a close eye on it lately, I expected somewhere between 7.6-7.8. Anyway, I added enough acid to bring it from 8 to 7.4 (32 oz). Tested again in an hour and it was still over 8.

This morning, I tested again with the same results. So just as a sanity check, I used my other OTO kit (uses R-0014 reagent), and it showed 7.2. This is much more in line with my expectations, since I really questioned my first test last night and put in a fair amount of acid.

So my question is which test to trust? If it really is 7.2, I don't want to put more acid in. But if it is over 8, I want to right away! The R-0014 is somewhat old (a couple years) but it has been responding lately, going up and down as I would expect.