Interesting. I would estimate that for me the time elapsed between sample collection and the pH test is usually under 5 minutes. I almost always conduct a FAS-DPD chlorine drop test first, using a 'speed-stir'. Even with a color corrected daylight lamp, when the chlorine is high ( 7-8 ppm+ ) visually matching the pH of the treated sample to the color standards is challenging.

At the very high levels of FC that you're reporting --15 ppm?-- the sample appears to greatly exceed the highest standard (8.2 using midget comparator) and is dramatically purple. Yet dilution of the sample with deionized water seems to correct for this... my pool water typically varies from 7.4 to 7.8 pH in the summer.

Taylor recognizes this as a potential interference for the test in K-2006C kits but doesn't mention dilution of the sample. Just tells the user to 'wait'...

Sanitizer levels > approx. 10 ppm may cause a blue-purple color resulting in false high readings. Wait for sanitizer level to decrease to normal levels and retest to assure an accurate reading.
http://taylortechnologies.com/produc...asp?KitID=2235


Nothing about pool chemistry surprises me anymore. The remaining mysteries are intriguing.