Conductivity Probe inconsistencies

djbetterly · Jul 30, 2015

So I've been running apex for some time, and until recently I've never had a problem with my conductivity probe. I've gotten to the point that I've completely isolated it from all other cables and the probe isn't even in the sump, its in the display tank. Everything was good, then suddenly I came home one day and it was ready between 32-33. Seemed odd, so I recalibrated. It calibrated to 35 just fine. Put it in the tank, immediately back to 32-33. I isolated the lines from everything, still 32-33. Decided to check my temp probe, that was off by a few degrees. After that the probe was reading fine for some time and now today, its back to 32-33 again. Right now its out drying out. I checked the temp, thats fine. THIS has become incredibly frustrating. I have no stray voltage, I've tested for that, I as well have a grounding probe. I'm kind of ranting, but I'm really really frustrated...

Also, is it me or does it seem there are a lot of topics about this lately. Is something up with the firmware?

I posted this on the Neptune forum as well.

hybridazn · Jul 30, 2015

How old is the probe?

Have you checked your salinity with another source like a refractometer?

djbetterly · Jul 30, 2015

The probe is less than a year old. I have a vee gee refractometer to double check. It's just frustrating that I've spent hundreds of dollars for the probe and module and it's inconsistent.

Terence · Aug 30, 2015

Calibrate your probe. Have the solution the same temp as your tank. Check afterward to see that it reads 35 in the solution on your display. Put 8oz of water from your tank into a cup. Place the temp and conductivity probe into that cup. Very lightly tap the conductivity probe repeatedly with your finger with the hole up on the probe so that all the air escapes. What it reads will be very accurate.

Remember that hydrometers and refractometers are not adjusting for temperature.

Also, a very common reason for errors is micro-bubbles. Sometimes the only way to see them in your sump is with a flashlight in a dark sump.

Is it possible your tank really was at 32-33 due to water loss from bagging corals for someone or some other loss of water?

BetURWrasse · Aug 30, 2015

@Terence

I'm going to slightly hijack this,

Should you set the temp compensate when calibrating??

Terence · Aug 30, 2015

Calibration will not be affected by the temp comp setting but the result in PPT will be so when the user wants to see a value (at the end) that makes sense, they should be using the temp probe if they are using temp comp.

Terence · Aug 30, 2015

BTW, we love having a forum here on R2R, but if you want to get a much better chance at someone in the community helping you out, I strongly suggest going over to https://forum.neptunesystems.com

ReefMadScientist · Aug 31, 2015

I have the same issue.

I even routed my conductivity probe all by itself so there would be no interference. My probe is 2 months old and will have to re-calibrate it. Not sure how it got knocked offline. My salinity is 1.026 but my Apex reads 31.8. Would be nice to trust that probe but I have been using my Milwaukee digital.

It only worked accurately for the first week.

Terence · Aug 31, 2015

Please read my posts above.

Also, please realize that often it is not the Apex that is wrong but instead the other device(s) you are comparing it to. My D-D refractometer will be quite a bit out of calibration simply by bumping it on the table. I have to then re-zero it. It would be even better if I calibrated my refractometer with Julian's accurasea product.

PedroYoung · Aug 31, 2015

I had a similar issue with the salinity trending downward. Moved the probe away from my heater and the problem went away. I think bubbles that were attaching to the heater were releasing and getting in the probe. In any case I would check for a source of bubbles getting into the probe. Air displacing water will make the probe read low.

ReefMadScientist · Aug 31, 2015

Terence said:
Please read my posts above.

Also, please realize that often it is not the Apex that is wrong but instead the other device(s) you are comparing it to. My D-D refractometer will be quite a bit out of calibration simply by bumping it on the table. I have to then re-zero it. It would be even better if I calibrated my refractometer with Julian's accurasea product.

I did read your other posts and will re-calibrate my probe. Just addressing that mine has the same issues for zero reason. I took the time to route it away from other wires, its solely by itself in a peaceful area of my sump, but the measurements just went haywire. I tap the probe to check for micro bubbles and still reads very low. Thank goodness I heat sealed my calibration kit or I would have to order another one.

Not bashing the probe or anything, I just do not have any positives with the thing so I cannot recommend it when people ask me locally how I like it. $125 is pretty hefty for this thing to be out of sync.

Sure, people may love it but I guess I am in the minority with this probe.

Terence · Aug 31, 2015

The most common issue ReefMadScientist is either:

a. There are microbubbles entering the probe.
b. The salinity really has dropped and the other method used to measure is not calibrated or accurate to enough detail.

Also note that your calibration solution can go bad too. Even if you seal it, it is not really "sealed" and can evaporate.

If I am checking on an aquarium with a probe that keeps reading off, the first thing I do is tilt it at a 45 degree angle (while still underwater), with the hole in the side up, and the tap it with my finger. If bubbles come out that is surely the reason.

Many people do not even realize the amount of microscopic bubbles in their sumps. You need to find a location that is calm and has as little bubbles as possible. Also, the depth and direction (angle) of the probe can help as well.

BetURWrasse · Aug 31, 2015

I think I got the best results by putting in the tank for a week and then using calibration solution. I also didn't fully dry off the probe, just lightly shook it first.

I notice on the BRS video they say to set the compensation to 2.2 when using the temp probe and attaching it to the PM2.

Is this accurate?

ReefMadScientist · Aug 31, 2015

Rsaalman said:
I think I got the best results by putting in the tank for a week and then using calibration solution. I also didn't fully dry off the probe, just lightly shook it first.

I notice on the BRS video they say to set the compensation to 2.2 when using the temp probe and attaching it to the PM2.

Is this accurate?

I too watched the BRS video and had compensated my Apex to 2.2 If I take my 2.2 off my probe is accurate lol I may have found my issue.

jduck · Nov 4, 2015

I had issues with probe dropping to 31/32 after calibration 4x. solution was 2 months expired but all were sealed
Even tried the plastic cup with tank water to see if there was any interferance. Still didn't solve the issue.

Double checked tank water with newly calibrated refractometer (used 2 reference solutions 30 and 35ppt) and it is 35.
So like many others I just re-calibrated probe with it in the sump. Now I don't have any issues. Reads 34.9