I've discovered an issue that is brand new to me after successfully testing and balancing my chemicals in the same pool for 3 years. For whatever reason, I can't get a pH reading that corresponds to the color shades on the vial. I've used three different brands of phenol red and I get a very bright red color and a very bright orange color...neither of the color shades matches anything on the vial. I decided to take a water sample to two different pool stores and one reading was 6.6 and the other was 7. I've never had this issue before and have no idea what is going on. Any ideas? Are there other chemicals that if out of whack can cause an abnormal pH reading?
I'm wanting to start the shocking process but really want an accurate pH reading before I start.