Does pH probe location matter>

Reefer911 · Jul 25, 2023

I have a new GHL pH probe that I keep calibrated but it constantly reads wrong. I check it with a Hanna pH meter, and although I don't completely trust the Hanna to be entirely accurate, the read out it gives me correlates with what I would expect to see. My ALK is 8.3 (salifert) and I am dosing AFR via GHL pump.

Back to the GHL probe, it has read 6.xx for quite some time and was in the sump where the drain connects to my Clarisea. This morning I decided to move the probe to the return pump chamber. During the day today, I look and its reading in the 9s so I know something's not right. Could it be a bad probe? I wouldn't think the reading would vary too greatly depending on location its placed.

I have inspected it and it is intact and clean. Also, I do not have a refugium in the sump.

Thanks

zheka757 · Jul 25, 2023

mostly no, but if I put probe on a bottom of my overflow box. ph. drops by .4 I showed a video of it long time ago, but no one cared about it. there is no movement of water on bottom of my overflow.

Reefer911 · Jul 25, 2023

Yeah it doesn’t sound right that the probe would sense that differently in those two locations.

WestMI-Reefer · Jul 25, 2023

I once had electrical interference with a refugium light located right next to the probe.
Besides that, and the flow mentioned above, I don’t think it matters much where you put it.

Sisterlimonpot · Jul 25, 2023

Reefer911 said:
I don't completely trust the Hanna to be entirely accurate, the read out it gives me correlates with what I would expect to see. My ALK is 8.3 (salifert)

Are you suggesting that there's a correlation between a specific alkalinity and a suspected pH?

And talk more about how after calibrating your probe you're getting "6.xx" in one location and 9+ in another.

Have you checked your tank, sump, overflow for stray voltage? How do you have the pH probe cable routed when you get 6s and what's the difference when you place it in a spot that gets 9s? Is the cable next to a power cord in one of those scenarios?

I'd personally start ruling out the easy stuff, and then start focusing on possibly a faulty probe.

Does the probe itself look damaged? Cracked... swollen... broken bulb... etc?

Randy Holmes-Farley · Jul 26, 2023

pH probe location can only make a minor difference in real pH unless flow is very low and you measure after a lit refugium vs before it, etc.

pH 9 is inaccurate, except right where high pH alk additives are put in, and only when adding them.

There are various sorts of electrical interferences that cna impact pH measurement, such as ground loop issues or itnerference from havign the cord near sources of electrical signals, such as mh ballasts, other cords, etc.