Apex Conductivity probe reading

[menglish]

I can use some help with this one.
I have calibrated both my refractometer (using 35ppt refractive index standard solution) and my conductivity probe (using 53,000 uSiemens/cm solution). After calibration, the apex probe reads the calibration solution as 34.9 ppt. When I place the probe in the tank, it reads my tank water at 28.3. The probe wire is isolated from the other wires, thus no electrical interference. With the refractometer, my water is 1.026.
My tank is maintained at 77-78 degrees.
Which measurement is correct?


I tend to trust the refractometer more

 

[DLHDesign]

Is the probe located clear of bubbles?
Is this from a PM2 or the main unit? If from the PM2, do you have a thermometer attached as well?
When you did the calibration, did you temp-match everything? Was the probe totally dry when you started?
Basically; this.

If all that sounds good, you may have some stray voltage in your tank that's causing it to read wrong when in the tank. Do you use a grounding probe?

 

[menglish]

The probe is run off a PM2 module and is located in the overflow away form bubbles. I re-calibrated it last night.
I did dried it off before i calibrated it and it measured the calibration solution accurately. Since i do not have temp probe connected to it, I did not selected any temp compensation.
I did exactly what was suggested in the BRS video.

 

[menglish]

No, I do not use a grounding probe. Was wondering if i should get one

 

[Caseyoidae]

Did you rinse the bulb in ro? Salt dries on there and gives bad readings

 

[kirbuno]

I recently had this same question and concern that perhaps my refractometer may by wrong. I contacted Neptune and got the response back that the conductivity probe is not measuring the same elements that the refractometer is. They evidently work differently.

 

[kirbuno]

Had to look it up again but here is part of their explanation.
"
The Apex probe measures the conductivity of the water, the refractometer measures the change in the speed of light when it goes from air to water, a hydrometer measures how dense the water is. These are 3 different things you are measuring, none of them is a count of the particles of stuff in a million particles of water. All 3 will give different readings if you dissolve different things, 35.0 ppm of sodium chloride will read different than sea water with 35.0 ppm of stuff in a refractometer.

 

[kirbuno]

They went on to say this:

To clarify, the conductivity probe functions by measuring the displacement of NaCl ions in the water. The Conductivity probe is not a refractometer. It's not going to read like your refractometer. This is common. It's a conductive sensing probe. Your refractometer is designed to detect specific gravity/density of all the salts in your water like KCl, MgCl, not just NaCl, but the conductivity probe will give you a closer look at the the true salinity (ppt) reading in your aquarium.


Typically most refractometers are not calibrated for Seawater, but a brine solution, thus they are reading the SG/salinity of many other salts in your water other than NaCl. So they will read slightly differently than a conductivity probe which only measures your actual NaCl concentration. Here is ant article on Reef Builders illustrating this discrepancy and points to another articlediscussing these differences. So it is not uncommon to see this difference between most refratometers and salinity probes.

 

[menglish]

Now i do not know what to believe. I tried another probe today and after calibration, it read the sal at 34.9 ppt and then read my tank at 29. Given how many people have been having this issue, i am incline to believe my refractometer. I will see about picking up an extra temp probe and then do a temp compensation on the calibration.
At this time i will just use the Apex sal probe for show and rely on my refractometer.

Much thanks all

 

[Jeepguy242]

i calibrate my refractometer with RO/DI

i then read the salinity of my tank and make my reefkeeper salinity probe match that... any other way and i have found that my probe drifts within a couple of days

 

[Scopulum Zombie]

Also having trouble with my conductivity probe.

Salinity 35ppt with refractometer.
78.5-79 F

Could you guys post the conductivity graph from your apex so we can compare data?

This is my last 24 hours.

 

[CindyKz]

Also having trouble with my conductivity probe.

Salinity 35ppt with refractometer.
78.5-79 F

Could you guys post the conductivity graph from your apex so we can compare data?

This is my last 24 hours.

This looks just like mine did. I moved it to a different area of the sump - problem solved. (It took me a long, frustrating time to get to the solution though, over 2 weeks.) I couldn't find any stray voltage so my assumption is that the return pump was causing electromagnetic interference. I didn't leave the return pump off long enough to test the theory.

I had an issue with my probe reading "high" - 36.1-36.4 on the probe, 34 on the refractometer. As it turned out, my calibration fluid was wrong (tested against several other bottles and brands). In reality my tank WAS at about 36.5. Now that I've correctly calibrated the refractometer it is all within 1ppt, which is as much as my eyes can see in the refractometer anyway. Luckily, none of my livestock or corals seemed to care.

 

[Vin's Reef]

This apex conductivity probe is highly unreliable. It's a constant struggle to get it to calibrate. The reading never settles even when dried out after cleaning with RO water. Then in if I go to the calibration solution and let that settle I put it in the tank and get a reading of 65. Ridiculous. It does this with 2 separate probes. Waste of time and money on calibrating solutions.

 

[Flexin]

Sad they still sell those probes...

 

[kirbuno]

I've had good luck with mine. I still check it against my refractometer about once a week but no surprises. Thing is when I first got my Apex probe I was shocked how far off it was even after I calibrated it. Then I contacted Neptune and found out it was because I was calibrating my refractometer at zero with rodi water and I should have been calibrating it with a reef calibration fluid meant for the hobby which is at 1.026, much closer to sea water. Don't use the Apex calibration fluid for this as the probe works a bit differently than a spectrometer and the calibration fluids are different. Found out my refractometer was way off. Not the Apex probe. The probe has been working great ever since.[emoji3]

 

[roberthu526]

I have the same experience. It will climb up after a few days but never reads 35. I only use it as a trend.

 

[Tiger-Paws]

I was having a great deal of issues with my salinity probe as well, I would recalibrate it and a few days later it would be way off.

Originally I installed the probe in the sump return chamber of my Red Sea Nano, but I tried moving to the top overflow coming out of the DT and a month later is has worked perfectly. when I see a reading of 34.8 I check it with my calibrated refractometer and it is right on (as best as my eye can determine.

I occasionally clean the probe by immersing it in a 2 gallon bucket of RO/DI water, within a couple of minutes it reads Zero and after placing the probe back into the overflow my readings return back to where that were before I cleaned the probe.

So far I have been very happy with my Salinity.

I would suggest that you look at your probe placement, Neptune's probes appear to be very sensitive to bubbles.

 

[Jonathan Iu]

I gave up on this probe. Trash.

 

[ca1ore]

They went on to say this:

To clarify, the conductivity probe functions by measuring the displacement of NaCl ions in the water. The Conductivity probe is not a refractometer. It's not going to read like your refractometer. This is common. It's a conductive sensing probe. Your refractometer is designed to detect specific gravity/density of all the salts in your water like KCl, MgCl, not just NaCl, but the conductivity probe will give you a closer look at the the true salinity (ppt) reading in your aquarium.


Typically most refractometers are not calibrated for Seawater, but a brine solution, thus they are reading the SG/salinity of many other salts in your water other than NaCl. So they will read slightly differently than a conductivity probe which only measures your actual NaCl concentration. Here is ant article on Reef Builders illustrating this discrepancy and points to another articlediscussing these differences. So it is not uncommon to see this difference between most refratometers and salinity probes.

That sounds like a load of bunk to me. Maybe the two devices will be a bit off, but 36 to 28 - I don't think so. If that is the case, then the apex probe is essentially useless. My approach has been to calibrate the probe with tank water rather than the little packets. That way I can 'force' the probe to read 35/36. It's not useful for absolute readings, that I use my refractometer for, but it is useful for alerting if the number drops or climbs significantly. Even in places where there's a low chance of bubbles forming, it's still good practice to give the probe a good shake every now and then.