ORP Probe recommendation

[ss88]

Can someone make a recommendation for an ORP probe model that is fairly reliable and compatible with neptune apex? Anything under $250 for the probe price point is acceptable.

I have two ORP probe styles, giving dramatically different readings in the tank water. Both reading within +-20mv of 400mv american marine solution when tested in solution. Not calibrated.

1) neptune apex probe with glass membrane covering the tip. (one year of service. Several years old.) reading 350mv

2) milwaukee ma921 lab grade double junction orp probe. (5 years old in original probe storage container. 1 day of service.) reading 120mv.

Attempting to run ozone for water clarity and help managing red slime algae. Phosphate and phosphorus register zero. Nitrate registers 10 ppm. Using hanna checkers. Would like to have three probes running to validate readings, one probe running on second controller. Trying to avoid ozone related catastrophe.

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[blaxsun]

From what's been stated, it's prohibitively expensive to calibrate the Neptune ORP probes. I do run a Poseidon 200 ozone system with the Neptune ORP probe as it's easy to program it to turn off the ozone off if ORP hits a certain level.

I'm running it at between 1.5-2.0 on the ozone dial for 18 hours a day into my Nyos skimmer (this is on a 200-gallon system).

 

[ss88]

From what's been stated, it's prohibitively expensive to calibrate the Neptune ORP probes

I agree, just checking if it was reading somewhat acceptable. Not calibrating.

both probes read +- 20mv of 400mv when in the solution.
385mv for the neptune probe
415mv for the Milwaukee probe


But when in the tank, I get the following readings
350mv for the Neptune
120mv for the Milwaukee.

Would be nice to have two probes within +- 20mv readings.

I’ll order two new neptune probes, if anyone else has suggestions on better quality probes, please chime in.

 

[ss88]

Poseidon 200 ozone system with the Neptune ORP probe

Using the same system as well

 

[taricha]

both probes read +- 20mv of 400mv when in the solution.
385mv for the neptune probe
415mv for the Milwaukee probe


But when in the tank, I get the following readings
350mv for the Neptune
120mv for the Milwaukee.

Take some tank water out in a cup and see what the probes read. There might be some electrical interference at play in your tank?

 

[Randy Holmes-Farley]

FWIW, I do not know much about the advantages and disadvantages of ORP electrodes that are more complex than a simple platinum tip.

For example, I'd not sure how the glass membrane is set up and what easily gets through it and what does not, but I worry about anything between the tip and the bulk water that is effectively filtering out what can contact the tip. What if it is selectively filtering out some redox active species and not others?