pH and ORP readings way off all of a sudden

[pclausen]

Thanks, I'll give that a try.

I just went through unplugging the probes one by one and this time my results were a bit different. pH and ORP readings fluctuate just by moving the wires near the controller. If I was a betting man, I would say that the ground on the ORP BNC connector is loose.

With all 3 connected, my readings were:

Temp 81.3
pH 7.91
ORP 393

ORP unplugged:

Temp 81.3
pH 8.11 (I believe this is the correct value)
ORP 458

pH unplugged:

Temp 81.3
pH 7.85
ORP 393

Temp unplugged:

Temp 22.1
pH 7.88
ORP 393

I'm not running ozone, so I don't think my ORP values could be pushing 400, or could they?

Here is a graph of last weeks readings prior to when things went haywire. As you can see, the ORP is steadily rising which I suppose could be normal for curing 200# of fresh rock in about 400g of water? pH readings look fine during that period.

 

[pclausen]

I left the serial cable unplugged all night, but no change was noted when taking readings this morning. I plugged it back in this morning (I like to be able to keep an eye on the tank from work) and unplugged the ORP probe. pH immediately jumped from 7.96 to 8.14 which I believe to be the correct value. I'll leave the ORP unplugged since I'm not running ozone yet as I'm more concerned with a proper pH reading right now.

With the ORP probe unplugged, the readings don't fluctuate when moving the wires around.

 

[pclausen]

I'm happy to report that my problem has been solved. It was dirty probes after all. The soft bristled tooth brush didn't really do a good job of cleaning the probes (calcium deposits from adding a Southdown sand been 2 weeks ago). But I found that using a pipe cleaner with a u-shaped turn on it was perfect to completely eliminate the buildup on the probes.

I'm still puzzled why moving the wires would so greatly affect the readings, but I guess you learn something new every day. Check out my graph since midnight. My kalk mix pump kicks on a 4am as can be readily observed. I also think an ORP reading around 300 is a lot more realistic.

 

[docjay]

And no more mirror image graphs either.

Jay