When to replace ORP probe?

[Quiverfull]

When should you replace the ORP probe. I know it is just for watching trends and the absolute number is not necessarily that important but I have had this one for about a year and I have noticed that it overall registers significantly lower than it used to.

[RussM]

Pick up a packet of ORP/Redox 400 calibration solution. You can't use it to calibrate the probe, but you can use it to check the probe. If it reads anything in the vicinity of 400, you're OK.

[Quiverfull]

I have not been able to find where you can obtain this. Any suggestions?

[slief]

I have not been able to find where you can obtain this. Any suggestions?

http://premiumaquatics.com/products/pinpoint-orp-redox-400-calibration-fluid.html?gclid=CPfV1t6n48gCFZWHaQodEcoBdg