PH Difference

Segal’s law is an adage that states: “A man with a watch knows what time it is. A man with two watches is never sure.”

Any pH in the 7's is OK. It does not make a difference which one you rely on.

The PH60 should be very accurate. But you have to make sure that it's properly calibrated.

With a new one, it might be a good idea to soak it for a day in storage solution and then calibrate it. They do put a drop of water in the cap and say it can be used immediately, but a refresher in storage solution can't hurt.

I actually always store mine in storage solution. I found that if I don't do that, it takes longer and longer for the reading to stabilise.

I also found that the reading can be slightly off if the tester and the water sample have very different temperatures. The tester will then apply the temperature correction based on the wrong temperature. But once the temperatures are equal within a few degrees (I'm thinking in Celsius here), the error should be less then 0.1. In winter, I prefer to dip the meter straight into the pool, so that the probe cools down to the water temperature, rather than the water warming up in a small sample volume.

I was always struggling with the colour test, but getting better with it. My impression is, that both test methods show pretty much the same result, nearly 0.3 difference sounds a bit much.

As Allen said, in this case it doesn't matter much. But I guess once you have a toy, you want to play with it, and gain some confidence.

It's also important to work "clean". When using the meter, I always first rinse it under the tap to get rid of the storage solution. Then I rinse it with pool water a couple of times before doing the actual test.

I actually think that it's more important to rinse it with the water to be tested, rather than distilled water as described in the manual. It's not that I only have a small precious sample, I don't have to stingy with pool water.

But I rinse it with distilled water and tap it dry before putting it back into the storage solution. Like that I don't contaminate the storage solution and can reuse it.

That difference to 7 seems a bit much. That might well explaine the deviation to the drop test.

There is a temperature dependency of the buffer solution's pH that the meter knows about. So, when you do the calibration e.g. at 50°C, then the meter should show 6.96 after the calibration. If you do it at 25°C, it should show exactly 7.00. It's important that the temperature of buffer solution and meter are not to different when doing the calibration. Don't just wait for the smiley face, but also make sure that the displayed temperature makes sense.

Try again. If it doesn't show pretty much 7.00 at std. room temperature, then order fresh buffer solution.

The calibration at pH 4.0 is more academic for pool purposes.

And soak it first in storage solution over night before you do the calibration.

And did you actually calibrate, or did you just dip the meter into the solution and it showed 6.86, but you didn't actually execute the calibration? After the calibration, the meter should (at 25°C) show the pH of the solution that was used for the calibration as 7.00 - that's what the calibration is for.

That's why it's important to soak it in storage solution to make sure that the sensitivity of the probe is right after storage/transport and then run the calibration. If it then still shows different results to the drop test, then order fresh calibration solution.

For pool use calibrating at 7.00 and 10.00 would provide more accuracy.