PH Probes

g6gang · Dec 25, 2014

Are there different types of PH probes? How do they technically work? Pros/cons?

My pH probe (2 months old) all of a sudden decided to report numbers in the 6's when it is really around 8.1. I guess I need to recalibrate? Is this common for only after 2 months?

electricrcplane · Dec 25, 2014

Two months seems too soon for a PH probe to lose calibration. They do need to be cleaned every 6 months or so in vinegar and would require a re-calibration. There is a lab grade PH probe that will cost more and has gone through more testing and has a smaller variance; I've had both and they're pretty close. Here's an explanation of how it works:

If you're using litmus paper, none of this matters. The basic idea is that the paper turns a slightly different color in solutions between pH 1 and 14 and, by comparing your paper to a color chart, you can simply read off the acidity or alkalinity without worrying how many hydrogen ions there are. But a pH meter somehow has to measure the concentration of hydrogen ions. How does it do it?
An acidic solution has far more positively charged hydrogen ions in it than an alkaline one, so it has greater potential to produce an electric current in a certain situation—in other words, it's a bit like abattery that can produce a greater voltage. A pH meter takes advantage of this and works like a voltmeter: it measures the voltage (electrical potential) produced by the solution whose acidity we're interested in, compares it with the voltage of a known solution, and uses the difference in voltage (the "potential difference") between them to deduce the difference in pH.

Randy Holmes-Farley · Dec 25, 2014

I don't think 2 months is too soon to recalibrate, but a pH in the sixes is not normal pH calibration drift. It may be electrical interference.

Let's recalibrate and see if it is working.

DaveMorris · Dec 25, 2014

I agree that two months is too soon as well as dropping to the sixes is not just a calibration thing...usually. Have you changed anything electrical inside your tank recently? As Randy mentioned, it could be electrical interference of some sort. Also, as with all electrical devices, they do go bad every once in a while. Maybe you just got a bad probe.