First sincere apologies if this is the wrong community, I don’t have lab science friends to ask about this.

Over the last few months my ph probe has been working well, then over a few days it started to drift down to reporting a ph of 2-3 instead of the 6-7 I would expect. There are so many cleaning procedures out there for ph probes, and knowing how to clean them depends on knowing what is causing them to foul.

I tried using generic probe cleaning solution, 0.1M HCL, and even just a light detergent. Nothing has worked so far.

I was reading that black spots on the ceramic could be from sulfides. And this probe is used 24/7 in my aquarium, where I dechlorinate freshly added water with a dechlorinate that I believe uses sodium thiosulfate. Could that be interacting with the probe’s silver /silver chloride?

I just got thiourea and I’ll be trying to prepare a thiourea/hcl solution.

What else should I try? What else might be causing this kind of fouling/errant results?