Testing pH when chlorine is high.

Phenol red is the indicator reagent used in all pool pH tests -- drops and strips. It's quite reliable, but it has a weakness: if the chlorine is too high, phenol red gets converted to a different indicator, chlorophenol red. With most phenol red drops, you can no longer trust the results one the chlorine gets above 5 ppm. Taylor's phenol red drops (in the K2006, the HTH 6-way and the K1000) have a compensating additive that makes them reliable up to 10 ppm.

The solution is simple: dilute with distilled water! For some complicated chemical reasons, you can dilute your sample 1:1 or even 1:2, without changing the pH enough to matter if you use distilled water. Tap water won't work; well water won't work, and normal bottled water won't work: only distilled or deionized water will work.

So how do you do it?

Just get a gallon of Walmart distilled water (http://pool9.net/distilled/) and a measuring cup. Add 1/4 cup of pool water, and then 1/4 cup of distilled water. If the chlorine level in your pool is really high, add 1/4 cup of pool water and then 1/2 cup of distilled water. Mix, and test your pH!

That's it!

Great tip. I'm printing this one out to keep with my pool notes for future reference. It'll really help when shocking during spring openings. :)

WOW, this is a great tip, just fond it. thank you so much PoolDoc