bad Ph probe?

[salty joe]

In June, I bought a Neptune 'lab grade' Ph probe to hook up to my Pinpoint Ph meter. It seems to need calibrated too often. The latest calibration lasted only 2 weeks. After calibration (I used Atlas calibration solution), 3.8 grams of borax in a liter of purified water showed Ph 9.28 instead of 9.18. Temp was very close to 77 F. http://web.archive.org/web/20021015005420/www.animalnetwork.com/fish2/aqfm/2000/feb/bio/default.asp

I double rinse the probe in RODI water between calibration solutions and am using a battery for the meter because I had interference when I used a wall wart.

Do you agree the probe is probably junk?

If so, can you recommend a decent probe?

 

[bertoni]

9.28 might not be that bad for that test solution. I'm not sure how accurate it should be. That's not very encouraging, though. I used an Oakton pH pen, so I have no experience with the more common probes. You could look at coleparmer.com for some ideas. They sell good equipment, although a lot of it is pricey.

 

[downbeach]

The only lab grade probe I ever owned was one from BRS used with a PinPoint meter. I calibrated the probe when I first installed it, and although I would check it every couple month's never had to recalibrate. I used PinPoints 7 and 10 solutions. Maybe you can find something in here.

 

[loudell]

Do you know that the term "Lab Grade" is a marketing term and in no way defines the quality of the probe?

Few people know this....

 

[downbeach]

http://www.bulkreefsupply.com/brs-lab-grade-ph-probe.html

 

[downbeach]

1. Some folks argue that a double junction electrode is preferable, and that is likely true. Without going into the design details, a double junction electrode makes it much less likely that there will be any exchange of ions between the aquarium and the filling solution through the glass bulb. This option may be especially important if you are using an internal reference electrode other than Ag/AgCl. For example, if it is a calomel reference electrode, it contains mercury. It is desirable to keep mercury salts out of the aquarium due to its toxicity, so a double junction is likely preferable in that case. Likewise, it is desirable to keep sodium and other seawater ions from entering the reference electrode, and a double junction prevents that to a much greater extent than a single junction. That aspect is more important if you leave the electrode in the aquarium water than if you put in into a storage solution after every use. In general, it is likely better to have a double junction than a single junction, but it may not result in appreciably better measurements.

From this article:


http://www.advancedaquarist.com/2004/2/chemistry#section-8

 

[salty joe]

http://www.bulkreefsupply.com/brs-lab-grade-ph-probe.html

Thank you for all that good info.

Did you leave this probe submerged in tank water 24/7? How long did it last?

With my luck, 'brand X' in Randy's article on calibration solutions is Atlas Scientific.

 

[downbeach]

Yes, the probe was left in the sump. The probe is about 4 years old now, previously I was using the standard probes, and was getting under two years of use before I had to replace them.

 

[loudell]

There are no designations like "Lab Grade" or "Standard". It is almost inferring cheap or inexpensive to expensive and costly.
My opinion would be to seek a probe with adequate internal fill Ag/AgCl and waterproof connections to the high suppression cable.

 

[bertoni]

If the probe is four years old, it's probably shot. I'd just get a new one.