ORP probe affects PH reading

[Submerged]

I have an ACII . My ORP probe, when connected, raises my PH reading from 8.2 to 8.45. I'm not using the serial connection. Inspection of the unit reveals that washers that separate the bnc connectors from the plastic ACII frame overlap (i.e., they touch). Not sure if this is normal...looks like considerable effort was made to position the two bnc connectors as close as humanly possible.

Is this a common problem?

 

[clp]

The ORP probe has a leakage current problem. Try cleaning with a soft bristled tooth brush.

Curt

 

[Submerged]

It did this right after I had cleaned it with vinegar and then a toothbrush. It also did this before the cleaning. It has always done this. I've just been subtracting two tenths to get a more accurate reading...

I suspect it has more to do with the AC2 unit itself than the probes. I tested the probes a month or so ago using a friend's AC2; on his AC2 the PH read the same, regardless of whether the ORP probe was connected or not.

 

[clp]

I doubt that it has anything to do with the AquaController. It doesn't matter if the connectors are touching as they are connected internally on the circuit board. You can do a simply experiment to see if it is the probe on the controller. Please each probe in a cup of your tank water. If the pH reads the erroneous value then it is the controller. If it reads the right value then it is the probe.

Curt

 

[Submerged]

Ok- you're right...it's the probe(s). Not sure which one. PH reads .2 to .3 lower when the PH and ORP probes are separated into different cups (which is the same as what it reads when the ORP probe is disconnected). It does this no matter how much I scrub/soak/clean the probes. The probes are 2 ft. apart in my sump. I can get them to be about 4-5 ft apart in the sump, but the PH probe still reads high so long as the ORP probe is connected.

Can you pass along some advice on how to remedy this?

 

[clp]

Sounds like the ORP probe needs to be replaced. Or as a hack you can adjust the calibration offset of the pH probe to read .2 lower. To do so go to the second screen of the selftest display. Press the up button twice, the down button twice, and then the select button. You should now be in the manual cal menu. Scroll to pH manual Cal, and adjust the offset down by .2 units.

Curt

 

[Submerged]

Ok- a couple followup q's then...

1. Would replacing the ORP probe affect the "drift" in ORP readings? Mine drifts upwards about 20-30 points per day. Not sure what is normal...I know they need to be cleaned frequently.

2. Will the ORP interference affect the PH reading by a constant number (e.g., .2) across the entire range of PHs I will encounter in my reef system? Or will the interference scale (i.e., will it be off more than .2 at a PH of 8.3 than, say, a PH of 7.8)?

 

[clp]

Once the ORP probe has gone through its break-in period a drift up of 20-30 mV is not typical. After cleaning a probe they usually read a bit low, and then after 24 hrs they stabilize.
I suspect that the offset would be pretty consistent across the small pH change in a reef tank.

Curt

 

[tack-msv]

I just purchased an ACII setup w/ new ph and ORP probes. The probes are at least 12 inches apart in my sump. I am getting the same readings (ph 8.45 ). I have a Milwaukee ph monitor w/ new probe (use it to measure my CA Reactor effluent). When I clean the probe and check the tank ph with the Milwaukee, I get 8.23. Since I know both probes are brand new and were calibrated with solutions from the same mix, should I just do the manual adjustment? Or should I demand a new ORP probe from the web source I purchased it from? All three probes, incidentally, are Neptune Systems probes.

 

[clp]

Please send an email to support@neptunesys.com.

Curt