ph mystery

[chem geek]

Assuming your Calcium Hardness (CH) is around 150 ppm or lower (you should test it to see what it is even though you don't need it to be high), then the only problem with the high Total Alkalinity (TA) of 250 ppm would be a tendency for the pH to rise over time. If you use a pool cover regularly you may not notice that.

As for the pH reagent, you generally want to use the proper reagent for the pH test you have since the blocks are calibrated in color for that reagent. Phenol red produces standard colors so you could add more of the reagent you have to make it more intense, but the reagent also has other chemicals (like thiosulfate) to neutralize chlorine that can interfere with the test. Such extra chemicals can affect the ph reading a little.

Richard