pH question

[Carolina]

I'm in NC, and I have an 11,000 gallon inground gunnite pool. It's been running over the winter, but I've been "neglecting" it the past month or so. I've always used a Taylor kit to check my water.

I recently went back to work after years as a stay at home mom. I work in an environmental laboratory, and have access to all sorts of fun equipment. Yesterday, I decided to bring a water sample to work for a pH check. My meter read 7.4, which seems a bit low given the fact that my pool's pH has a tendency to creep up if I don't stay on top of it.

I did a comparison using my Taylor kit, and that reading was 8.2. This is a huge difference.

I'm stumped! Any thoughts?

[Goolsbymd]

How long was the water sitting in the sample bottle for also was everything clean before adding the water to the test bottle, kit, and so forth? Also when did you buy your Taylor kit?

[Carolina]

Taylor kit is approximately 8 months old. I tested the water via Taylor immediately. At work, there was about a 10 - 15 minute lag time between sampling at my home and testing at work. In both scenarios, equipment, vials, etc are either unused/ new or cleaned thoroughly.

The only other variable might be that I didn't let my sample at work equilibrate long enough, such that the reading wasn't actually stable. I dunno, though.

[kelemvor]

When was the last time your pH meter was calibrated? I ask because I've seen admins here repeatedly mention that unless electronic pH testers are calibrated "very frequently" (although I don't know exactly how often that means) that they can be quite unreliable.

My k-2006 is a year old now and seems to give reliable results (it jives with what the guys at the pool store generally test at). You could always just get a new reagent for your taylor, or even a "basic" kit from taylor or lamotte for under 10 bucks.

Also, what are your other readings for the pool? Things like high CL can affect the pH test.

[Carolina]

The meter is calibrated immediately before testing, with a 3 point curve - buffers 4, 7, and 10. Calibration is also verified with a second source standard, as well as a QC sample with a known value. I'd not trust a value unless it had been calibrated within 24 hours or so. That being said, the value would only be off probably by 0.1 or so... my home kit is based on a color comparison, which is more subjective.

Maybe my home kit has gone bad.

[kelemvor]

Given the price, you could probably just replace the phenol red reagent. I believe it's this one: http://www.amazon.com/Taylor-Replace.../dp/B0002IXIL8 for $2