Problem with pH probe or something

Basic / Standard Reef Angel hardware

Posts: 66
Joined: Fri May 05, 2017 11:27 am
PostPosted: Sun Jul 02, 2017 7:57 pm
I re-calibrated my pH probe today and when I put back into the tank, I got a reading of 2.something. I was in a hurry and figured I screwed something up so re-did the calibration a short time later. The second go-round, I didn't pay attention to the Uapp readings when calibrating 7.0 but when I was doing 10.0, the Uapp display was reading 10.05 when my calibration numbers stopped changing while calibrating 10.0, which makes sense. My calibration numbers ended around 550 for 7.0 and 850 for 10.0. All seemed well until I put the probe back in the tank. The pH started dropping and is now back to 2.64. I rebooted the controller, and it made no difference. My pH probe has been working for the last month (ever since I set it up). However, while I was on vacation, my pH started toggling back and forth with about a .07 or .08 difference. For instance, it might read 8.22...8.23...8.16...8.23...8.22...8.15...8.22 and so forth. When I came home, I rebooted the controller, and that went away. However, I wasn't confident in the reading so I re-calibrated today. After the re-calibration, it all went to pot.

Please help.

Posts: 12424
Joined: Fri Mar 18, 2011 6:47 pm
PostPosted: Mon Jul 03, 2017 10:15 am
What happens if you place the probe in a cup with tank water?

Posts: 66
Joined: Fri May 05, 2017 11:27 am
PostPosted: Mon Jul 03, 2017 11:15 am
I found the cause... if you insert the probe all the way into the probe holder to where the probe's adapter is resting on the holder (e.g. as far as the probe will go in the probe holder), the reading plummets, leveling off at around 1.42. If you only insert the bottom inch or so of the probe, the readings make sense, but they aren't accurate (getting around 7.96-8..01). Note: I'm topping off with concentrated kalk, and my readings have mostly been in the mid 8.2's-8.3's.

I figured the probe casing was allowing water to get in so I tested in a cup of RO/DI water... similar issue. If I put the probe all the way down to the adapter in the cup of RO, pH decreases. If I lift up, to the last inch of the probe, pH increases, though the swings are a lot less than when in saltwater. I suspect this probe has had this problem from the beginning. When the guy helping me inserted the probe into the holder initially, he pulled just enough slack to where the probe leaned in the holder, and only maybe an inch was in the water. After we re-calibrated yesterday, we put the probe all the way in the holder, and the pH readings plummeted.

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