Apex conductivity probe issues

dacostas

New member
So I bought a new apex and received it earlier this month. I've had nothing but trouble with the conductivity probe ever since.. It reads just under 32 ppt and I have contacted Neptune about this. After some back and fourth they told me:

"You calibrated it with solution it read 34.9~ this is normal. Broken probes would not read this well if they were non operational. Then placing it into your sump you get lower salinity. The probe is going to read what it gets based on the distribution of ions in the water it's sitting in. You cannot compare it's reading to anything else. Nothing with read number to number to our probe. Than after seeing this low number you moved it back to the bag of solution and it read 34~ again.

The probe is working as intended. The probe reading 31 in the sump is normal. As I mentioned. Our probe will not reflect values you see in refractometers or any test kits. It's a PPT reading of our own. It's operating normally."

I've tried everything from separating the probe from all wires, turning off All equipment minus apex, testing in a cup of tank water (so no flow, microbubbles, etc.), and if I add the probe in calibration solution it reads correctly. On 2 refractometers, they read 35ppt. My probe reads just under 32 in my sump and they say this is normal? It doesn't make sense why someone would be willing to spend so much $ on a system and one of the most important "levels" don't read properly? This is my first controller system so I have nothing to compare against but it doesn't seem right. I feel like I'm getting excuses by Neptune. I have tried every suggestion on forums for 2 weeks now and have recalibration a few times with a new calibration solution every time.

Thoughts? Suggestions? Thanks.


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Calibrate it in sump. The probe is good to tell you if salinity is off, but dont rely on it for anything important.
 
Did you match the temp of the calibration solution to that of the tank water? To me it sounds like your temp compensation is off. That or you are getting micro bubbles in the probe tip.
 
The other thing that can cause issues with probe readings is stray voltage and or interference. Since it reads correct in the calibration solution, the probe is in fact working correctly. You either didn't match the calibration fluid to the waters temp, have micro bubbles in the water, interference or stray voltage. I normally float my calibration fluid in the tank water and do the calibration with the solution in the tank water as well with the solution in the same are of the sump that the temp probe is located. That helps to insure temp compensation is correct.
 
The other thing that can cause issues with probe readings is stray voltage and or interference. Since it reads correct in the calibration solution, the probe is in fact working correctly. You either didn't match the calibration fluid to the waters temp, have micro bubbles in the water, interference or stray voltage. I normally float my calibration fluid in the tank water and do the calibration with the solution in the tank water as well with the solution in the same are of the sump that the temp probe is located. That helps to insure temp compensation is correct.



Thanks for the help. I did float the calibration in the sump for about an hour and did separate the wires from all other equipment. I even went as far as turning everything off minus the controller with no luck. I even tried in a cup of tank water along with gently tapping to make sure there were no microbubbles. No luck. I've called BRS and they said it's an ongoing issue with many types of conductivity probes. I've decided to just monitor it for big changes that could mean an Ato failed, etc. ty!


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So I bought a new apex and received it earlier this month. I've had nothing but trouble with the conductivity probe ever since.. It reads just under 32 ppt and I have contacted Neptune about this. After some back and fourth they told me:

"You calibrated it with solution it read 34.9~ this is normal. Broken probes would not read this well if they were non operational. Then placing it into your sump you get lower salinity. The probe is going to read what it gets based on the distribution of ions in the water it's sitting in. You cannot compare it's reading to anything else. Nothing with read number to number to our probe. Than after seeing this low number you moved it back to the bag of solution and it read 34~ again.

The probe is working as intended. The probe reading 31 in the sump is normal. As I mentioned. Our probe will not reflect values you see in refractometers or any test kits. It's a PPT reading of our own. It's operating normally."

I've tried everything from separating the probe from all wires, turning off All equipment minus apex, testing in a cup of tank water (so no flow, microbubbles, etc.), and if I add the probe in calibration solution it reads correctly. On 2 refractometers, they read 35ppt. My probe reads just under 32 in my sump and they say this is normal? It doesn't make sense why someone would be willing to spend so much $ on a system and one of the most important "levels" don't read properly? This is my first controller system so I have nothing to compare against but it doesn't seem right. I feel like I'm getting excuses by Neptune. I have tried every suggestion on forums for 2 weeks now and have recalibration a few times with a new calibration solution every time.

Thoughts? Suggestions? Thanks.


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While 32PPT (using Apex conductivity to density conversion) seems low for a tank truly at 35PPT, this is not crazy, especially considering how most refractometers are calibrated. Your post doesn't give your method of calibration, so I'll just post a link to Farley's thoughts on calibrating a refractometer and you can decide for yourself how close or far from 35PPT your actual test are:
http://reefkeeping.com/issues/2006-12/rhf/

The above said conductivity does not measure the amount of NaCl in the water, it measures the ability to for current to flow through the solution. So consider all of the elements that make up seawater typically measured in μS/m not PPT. Since the average (where we collect our specimens, therefore hopefully your salt mix) is 53,000μS/m, so Apex converts this to 35PPT.

The refractometer doesn't actually measure NaCL PPT either, it measures the refraction of light passing through the lens and the water, again the calibration solutions do a similar function of Apex, which is to get s similar refraction to natural sea water at a specific temperature.

If you understand the two paragraphs above, I apologize for the run-on, but, it's important to have the foundation of the tests to understand where there could be a discrepancy. I run two of most probes in my tank and in different areas and constantly compare the results, much like you have two refractometers. The probe will go bad, and ever now and then Apex ships a bad one, so it's still possible your probe is bad. This said, if you buy a spare probe or even dual like I have and they both show 35ppt in the same 53,000μS/m calibration solution, I would suggest at 32PPT your tank's conductivity is ~48,500μS/m. This doesn't mean your NaCl is low, perhaps your dKh is low or one of many other elements that make up seawater is different in your tank.

Now... how important is it to be at 35ppt or 53,000μS/m exactly? I would argue not at all, as long as your in the ballpark and consistent. 32PPT may be a little, low, so double check your refractometer calibration procedure and temperature of the calibration solution and if your meters temperature compensate and how. If you determine that with very high confidence that your tank is 35PPT, then double check the probe or even bring a sample of saltwater home from your LFS (reef system, there fish systems are typically intentionally kept low) and test your probe, if it shows 32PPT or less, it's likely defective. As others have said stray voltage, coils, power cords, etc can interfere, I haven't personally seen that issue, but, I'm sure it's possible, so test in a glass to remove the variable.

If your tests show the probe to be 33 to 36 maybe even 37, I would say make a note of the refractometers showing 35 and the probe showing 33 and call it normal. The probe is great to constantly see where your system is as far as consistency. If you don't have an ATO you will see as much as 2PPT between daily top offs. When your lights go out conductivity will change sometimes by as much as 1PPT, due to conductivity of CO2 vs O2 and plankton in the measurement. A refractometer isn't typically able to help you visualize this.

Here is another link (not reefing related), but, showing/explaining the difference.
https://www.appslabs.com.au/salinity.htm

I hope this helps,
JW
 
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