# Pinpoint pH meter



## scuba guy (Feb 10, 2007)

I recently bought a new Pinpoint pH meter and noticed that it takes quite a while for the readings to settle down when you place the probe in a new solution. I was wondering how long is reasonable to leave the probe in a new solution in order to be sure of an accurate reading.

My aquarium was reading 7.4 (Kh = 15) and when I placed the probe in distilled water (that you buy for irons), the pH went UP to about 8.3 and then settled down to 6.5 - quite a swing. Puzzling?

I placed the probe in the 7.0 calibrating solution and it jumped to 7.8 then 7.5 then 7.2 .. 7.07 .. 7.03... 7.02 and it is staying at 7.02. The whole process is about 10 minutes....Is this normal? It hasn't moved off of 7.02

Thanks


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## Cavan Allen (Jul 22, 2004)

Do you have a grounding probe? Those can really help the readings settle down.


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## scuba guy (Feb 10, 2007)

What is a grounding probe?


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## t2000kw (Jul 29, 2006)

This might help. It's a probe in addition to the actual pH measuring probe that prevents small stray electrical currents from interfering with your pH measurement. This tells how to use the one supplied with the unit. It is an instruction manual for a Hanna pH meter. Apparently not all probes come with one.

www.hannainst.com/downloads/instr/ist981401n.pdf


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## yxberia (Apr 19, 2005)

> I placed the probe in the 7.0 calibrating solution and it jumped to 7.8 then 7.5 then 7.2 .. 7.07 .. 7.03... 7.02 and it is staying at 7.02


This shows that grounding probe is not the factor. Else we will need grounding probe in calibratin solution too ?

1. Some pH tester has temperature compensation built-in. So it will take some time to recalculate when temperature changes.

2. It is also advisable to stir and move the probe around to increase contact between probe membrane and water. This will also remove air trapped. Then you will get your reading much faster.

3. Keep the prob moist (preferably with buffer solution) and firmly capped all the time. Else it will lose its sensitivity.


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## Mr.pH (Nov 12, 2006)

In my experience it is normal that electrode needs some time to stabilise - say up to a minute. Note that electrode is the weakest part of the measuring system and its quality is the most important factor in measurements. IMHO several minutes is a slow response, but as long as you are able to properly calibrate pH meter - don't worry (unless you are in a hurry  ). Chances are the situation will change when you buy a new electrode, and that's a thing you will not avoid. No idea what is a recommended lifetime of the one you bought with pH meter, but usual life span is somewhere between 9-12 months. After that time you will be probably not able to calibrate the pH meter at all.

Was there any temperature difference between electrode and solutions? If so, initial drift can be at least partially assigned to electrode changing temperature. But it shouldn't be almost a unit change.

Visit pH meter site (see signature) for the wealth of pH measurement information. Some will be of no use (I doubt you are interested in Nicolsky-Eisenman equation  ) but huge part of the site is strictly practical.


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