PH Testing Question

[johnnyp0_4]

Hello all,

New pool owner, I have been doing the BBB method since start-up (Nov 06). The water has stayed pristine and beautiful since day one. So many thanks to all of you for this wonderful forum.

I have been using a Taylor 2006C test-kit for all my testing, and here are my numbers:
Water Temp - 72F
FC - 3.5
CC - 0.0
PH - 7.6
TA – 130
CH – 180
CYA - 35

I have two questions, both concerning PH. The first question is this. Several weeks ago, in an effort to see how repeatable the test results were, I tested everything, and then re-ran the tests. The results from the second set of tests matched the first pretty well (within 1 drop of reagent) except for the PH. The PH reading on the second test was about 0.5 to 0.6 higher than on the first test.

Since that time, I have been testing the PH twice every day, and consitantly the PH will be 0.5 to 0.6 higher on the second reading. As an example today my first reading was 7.0, the second test reading was 7.6, the third was 7.6. I have verified that the readings stay constant after the second test.

At first, I thought perhaps the PH indicator solution was bad, so I purchased a new bottle but I get the same results. I then thought maybe it is my color perception, so I had my wife read the results with the new bottle as the old. She came up with the same numbers as myself...Can someone please explain to me what is going on?

My second question concerns PH stability. The PH in our pool (Pebblesheen finish) has stayed relatively constant for the last month without any intervention on my part. Is this normal?

Thanks,
John P.

[waste]

Hey John, welcome to the forum!!

The only scenario which I can think of right away is interference from another test. Let me explain what I mean - the 44 ml side is used for pH/ TA and CH, if you do the pH after doing Alk or CH without completely rinsing the chamber, some of the other reagents may be present in sufficient quantity to lower the pH reading. I'll assume that subsequent (higher) tests are done without having run the other tests - therefore an accurate reading. I imagine that if you're dumping the test water back into the pool where you are taking the samples that similar interference could occur. That's the best theory I could come up with in 5 min. Perhaps someone else has an alternate theory (Waterbear may well have better insight into this)

While I don't know much about pebblsheen, I believe the pH rise only occurs when the material is curing - perhaps it's fully cured.


Again, welcome to the forum - Waste

[johnnyp0_4]

Waste,

Thanks for the quick reply

Your statement about a previous test interfering with the results of the PH test are certainly a scenario. I have been following the procedure on the lid of the Taylor test kit, which has you checking for Chlorine and then PH. So I can certainly alternate the test sequence.

I have not been dumping the results of the Chlorine test back into the pool, and I thought I had been rinsing the tube before doing the PH test well enough, but maybe not enough

I will try doing the PH test first tonight, and then post the results here.

Once again, thanks for your help.
John

[jnorris]

I'd like to know what the OP's solution to this is. I use the Taylor kit, and my PH test do the same thing. I've started doing the ph test first, to make sure there is no interference from a previous test, but the same thing happens. For instance today, first test was 7.4, second test was 7.8, third test was 7.8. I've had it vary as much as 0.8 ppm.

Any other guesses? Maybe I need a new reagent bottle (just received test a month ago)?

[chem geek]

There have been 2 (if I count them correctly) reports of this varying pH problem (one on the TroubleFreePool site) with the first test being the one that is different from subsequent tests. I don't know what is going on, but will describe what I do and I'll have to test multiple times to see if I get any variation (I think I've done that a few times and don't recall any variation). Whenever I take a pool water sample, I flip the comparator tube upside down and put my hand about a foot or so (probably 18") below the water surface and then flip the tube so it becomes upright and fills with water. I then take the comparator out (now filled with water), then invert it and dump the water back into the pool. Then I go down again (inverted) and repeat to get a water sample. This sample is the one I then spill out excess into the pool (to get to the appropriate line, which for pH is the 44 ml line near the top). I cap the tube (which I rinse in the pool water first) and then take it back for measurement, adding the 5 drops, capping, inverting a few times, then looking at the color. After I'm done with the test, I dump the sample into the sink and rinse out both the tube and the cap with filtered water (though tap water should be fine -- we just happen to have a filtered water faucet at the kitchen sink where I do my tests so I use it).

If the sample is shaken instead of inverted, then it's possible for the aeration to make the pH rise a little. That's one possibility, though doesn't explain why only the first sample is off. It could be that though the tube is cleaned, the cap is not. That would tend to make the first sample bad if the previous test was not a pH test.

Richard