best ph probe for accuracy, longevity, and price?

[jasonkola]

I got a ph controller. but now I am trying to decide what probe to get for it. I have read a little about probes on the net so I know the basics. my controller accepts probes with a bnc connector. I have found alot of expensive and a few cheaper probes out there. I have found the american marine pinpoint and a neptune ph probes that both claim an accuracy of .01. which is good. and they are priced ok but I couldn't find any info on there longevity. I know they have to be replaced every so often but I dont want to get one that has to be replaced every 6 months. any input on this subject would be greately appreciated.

[PatMayo]

I have a pinpoint as well. I think the probes last at least 2 years. My only complaint with mine is that it seems to need calibrating every 2 weeks or so. That's quite a bit in my estimation.

I think Randy did some testing of ph probes etc. here they are, maybe they will help.

http://www.advancedaquarist.com/issues/feb2004/chem.htm

http://www.reefkeeping.com/issues/2005-02/rhf/index.php

Regards,

Pat

[Randy Holmes-Farley]

The Pinpoint is fine, as are many other brands. I have used many different types, and discuss probes a bit in the article above. I'd generally recommend getting a sealed gel electrode, rather than one that requires filling as that also presents an opportunity for something to go wrong (admittedly, at the moment I am using one that is refillable).

Cole Parmer sells lots of types: www.coleparmer.com

[jasonkola]

thanks for the info. how do you know when it is time to get a new probe? also recalabrating every 2 weeks dose seem like a lot. is the pinpoint a double junction probe? I was looking at the colepharmer double junction probe for 60 bucks. it might be better to get the $60 probe if it last longer and dose not have to be calibrated so often.

[Randy Holmes-Farley]

how do you know when it is time to get a new probe?

When it can no longer be calibrated, or responds very, very slowly. You only need to recalibrate as often as necessary. I rarely do it because mine doesn't drift between calibrations. That can be determined by trial and error. I would not assume that more expensive probes necessarily need less frequent calibration.

[rick s]

Randy,

Mine repeatedly drifts +.17 over 6 weeks. Is the drifting a function of the probe or the meter?

What meter and probe do you have (since yours doesn't drift)?

[Randy Holmes-Farley]

Drift can be either. Right not I am using a Chemcadet pH controller (from Cole Parmer, but probably discontinued as it is more than 5 years old) as the meter and an Orion pH probe that is probably overkill in terms of expense.

Is your probe in the dark? Algae growing on it might make it drift faster. Does it always drift the same direction?

[rick s]

<a href=showthread.php?s=&postid=7444258#post7444258 target=_blank>Originally posted</a> by Randy Holmes-Farley
Is your probe in the dark? Algae growing on it might make it drift faster. Does it always drift the same direction?
I've had it in a few different places in my sump. No light on it at all. It always appears clean and I toothbrush clean it every few weeks or so. Yes. It always drifts positive. I am going to calibrate it again in a few weeks which will make it 6 weeks total again. I'll let you know how much it drifted this time. It looks like this topic (pH meter drift) would be a good test study.

[Randy Holmes-Farley]

yes, let us know how it drifts.

good luck :)

[Justjoe]

Randy,
I just posted this reminder to the LIRA members and its relevant for this discussion.

"Don't Trust Your Meter Reminder!
Hey,
Its about that time I send out the:
"DON'T TRUST YOUR METER" reminder...
While most are trustworthy, even the good ones go bad.
I recently changed my kalk dosing routine and saw a quick climb in my pH, so I re adjusted my dosing. Something didn't seem right and my Salifert kit alerted me that my probe may not be completely honest with me, even though it would still calibrate well... so which one was lying to me?

Here is some interesting text from Craig Bingman on probe life, salt water and how they may interact over time:

"pH electrodes read high after long continuous duty in saltwater systems.
Replace the electrodes every six months or so. It isn't a problem with the meter, it is really an electrode issue. More precisely, it is an issue with old electrodes with a weak internal solution, and the salt concentration of the NIST standard calibration solutions. If the NIST solutions were a closer match to the salt concentration of seawater, this junction effect would be nulled out in the calibration process.
However, NIST calibration solutions are all you are likely to get on the market, so you just need to change out the electrodes every six months or so to get reasonable performance".
So new probe installed and it read closer to the pH test kit and all is fine. A new pH controller on my kalk dosing pump (to safeguard overdosing) will act as a second meter to watch over my reef tank pH.
Joe"

I normally see probe life of about a year from the Pinpoint probes, sometimes longer. If you need to calibrate a probe often, I would get a new probe.

Joe

[Randy Holmes-Farley]

:thumbsup:

FWIW, in the absence of limewater, high pH is almost always a pH measurement problem. ;)