Man you know your stuff! I believe you've nailed it. My ORP probe was bundled in my cable management system with the cord from the Varios pump on my skimmer. I'll know soon but I think that's it. btw, is my system grounded if all my electrical is plugged in to grounded power strips, which are plugged into GRFI outlets?
Oops! That didn't fix it. With each of the past two feedings the ORP shot up 30 mv's IMMEDIATELY upon shutting down my skimmer and return pumps, and returned just as fast to the prior level when the feeds finished.
The probe is in the sump. No food or water from the display enters the sump during feeds. I feed frozen three times a day. On the attached graph from today, at 0600 skimmer and UV off for four hours after phyto & MB7 dose. 0800 slight bump as returns off for feeds. Gradual decline until 1000 bump when UV and skimmer go back on. Other spikes are with noon and 1600 feeds. Not sure of cause but it does seem electical.
Through process of elimination it has nothing to do with either. I have two COR-20 return pumps one of which is dedicated to the UV unit. It appears switching this pump off triggers the ORP spike. Not sure what that means however I've already had to replace one of my pumps and this is the newer one. Neither is over 8 months old.
I tried moving the probe to the opposite side of the return chamber from the pump but nothing changed. The only thing else to try is going behind my control panel and separating that cord from others. Now that I know it's electrical interference and my sump ORP isn't actually changing I'm not sure it's worth messing with.
Didn't do ANYTHING ! I have since determined the ORP rise occurs whenever the UV STERILIZER is turned off. Has nothing to do with any of my pumps but since the UV is programmed to shut off in the absence of flow I was misled. The skimmer output does not return to the sump therefore it must be some kind of interference. I wonder if the true value is the one I get when the UV is on, or off.
Well after several false steps I truly believe I have the answer. UV is the large vertical tube on the right. ORP probe is in the return on the right side of the sump but moving it had no effect. This morning I ventured into the maze of wires in the back of the white control board and found a lot of coiled ORP probe wire and UV cord in close proximity to one another. Since I rerouted the probe wire removing it from the box my readings have stabilized. I don't know the physics behind it but happily the higher values appear to be the accurate ones. My ORP is now peaking out at 330 rather than 290-300. Somehow when energized the UV transformer or wires have been suppressing the values.
