Calibrating PH Probes What a PIA

[hilde123]

I have struggled with calibrating PH probes since I've installed my AC3 3 years ago and replaced probes 3 times. I have the AC3 with one PH probe and one ORP Probe and PX1000 with one PH probe. Originally I think I had a ground loop issue caused by a pressure switch that was not isolated on the IO connector that was causing the issue. That was 1.5 years ago and while I dont have the stability issues, I cant get accurate readings and the Probes drift .4 PH over the course of a month or two. I have tried many combinations of calibrating both probes (1) both PH probes together in cal packets (2) Both PH probes and ORP probe in cal packet (3) Both PH probes and ORP in cal packet and wire immersed in cal packet and immersed in sump (in case there is an electrical leak) and I cant get a good calibration. After calibrating I put them back in cal packet and they read usually .3 PH low. I just again calibrated and the AC3 says my tank is 7.75 but 3 chemical test kits say between 8.0 and 8.1. I am most worried about the accuracy of my 2nd PH probe (in the PX1000) as it controls the CO2 in the calc reactor and I need it to keep the right PH to dissolve aragonite. I've honestly given up. I have been using Pinpoint PH probes and dont know if that could be causing a problem. I used to have one Neptune PH probe but it didnt hold up too well in the calc reactor (after 6 mos it turned all black from the tip up 2" inside the probe) dont think it is pressure rated.

I would like to know if anyone else is experiencing the same problems or have found a solution. Thanks

[laverda]

It does not sound like the problem is calibrating them per say.
My probes have been very stable and most are way past there recommended life. PH probes are recommended to be replaced I think every 6-9 months for standard and 9-12 months for lab grade. That said, I think all 3 of mine currently are about 2 years old. I took a forth one off line recently, as it was not maintaining calibration and over 2 years old also. The older they get the more the less they will hold calibration. Also they should be cleaned in vinegar every 2-3 months, depending on your system and always before calibrating used probes. Just soak them for 15 mins then brush the tip gently with a old tooth brush and rinse.
You do need a lab grade probe for inside a calcium reactor to handle the pressure.