Bad ORP probe or something else?

I think my ORP probe has gone wacky - but I'm not sure. How do you test things like this? About 7-8 days ago the ORP started a downward trend, and every day since then between 10 and 11am the ORP takes another noticeable dip.

I can't find anything that seems to correlates with the falling ORP other then two recent events.
First I installed a heater (since it's starting to get cold) but it's on/off cycle does not seem to match up to the OPR drop.

Second, I had a strange episode of sticking/clumping bio pellets in the BioPellt reactor that has recent stopped. It has not done than in more then months (4-5 to be exact)

Third - I feed everyday between 9 and 10:30, which sometimes matches up with the morning OPR drop, but nothing about hat schedule or the food I fed has changes in more than year, and the current batch of food (I feed frozen Mysis) I'm using pre-dates the recent OPR drops.

EDIT: I should add - all the coral, fish and other inhabitants all look and are acting normal

In your opinion, is it a bad Probe or something else?

Here are a few graphics form my Apex

 

That is strange. When was the last time you calibrated it? Inspect it?

 

I have never calibrated it since the instruction I got when I bough this probe said it didn't need it. I also inspected it and it all look normal(ish).

With that said, I tried a little experiment. I shut down the main return pump, which is a Waveline DC6000, which was installed back in March. I run it externally, so it's not in the water. But - when I shut it off, the OPR almost instantly jumped to 280+. So I turned the pump back on, and it dropped to 244.

I then moved the probe to the display tank and performed the same procedure. I got pretty much the same result. With the pump off, ORP would settle in around 279-286, with it on, it dropped to the 240s.

Next I tried with the pump not off, but set to the lower speeds. At the lowest speed, I got the same result, at about 1/25 of speed, it started to Drop the ORP.

Since the Pump is external, I don't see how it could leak current, but ,could a bad power supply cause this? Granted the power supply is somewhere behind the tank and at least 3-6 feet from the probe.

 

I think the mystery lies right here:

If they're no longer clumping, they've probably started working much more efficiently, and you're seeing it in ORP. At a minimum, not clumping is going to make them work "differently".

 

I agree - it did sort of coincide with that event, but I'm not fully convinced they where related. I did have a huge PH swing on Halloween night which you can see on the first graph, do to many breathers in the house (we had a party). The downward trend started a day or so before the party, but the pellets started clumping the day after the party.

....aquarium stuff is hard :-/