Apex Salinity Probe Calibration

[n2585722]

Yep! I have a miluakee digital refractometer as well as standard solutions to confirm its accuracy. That is what I go by. So when my actual ppt is confirmed to be 35, I just calibrate it in the sump. I am thinking that there is electrical interference in the tank stand or other factors that make the universal calibration fluid not so universal.

One way to know for sure is to place the probe in a cup or glass of tank water and see if you get a different reading than it has in your sump.

 

[spifftempo]

If you are concerned more about the precision of the number and less the accuracy, then it is fine to use tank water instead of the calibration standard. So at the point when the calibration says to place the the salinity probe into the 53 mS/cm solution, place it into your tank instead where the probe will be mounted. Take the same care to make sure there are no air-bubbles on the probe monitoring surface. This does help to offset if there is stray voltage or EMI in the area of the probe. Realize that doing it this way, means the probe will show 35.0 ppt in your tank whether or not that is an accurate representation of your salinity or not.

With that being said, if you are concerned about the accuracy, then using the calibration solution is a better solution. If you have uncontrollable EMI or stray voltage, then placing the probe in a cup of tank water removes all that. Calibrate the probe using the solution confirm the calibration is accurate (it should read 35.0 ppt in the solution). Take a cup of tank water and place the probe in the cup.

 

[DivingTheWorld]

With my calibration, I'm not concerned with stray voltage, which is why I calibrate with my probe in my sump. My concern (and it sounds like many have this concern), is that calibrating with the solution as suggested by Neptune does not work. It is inaccurate. As soon as I pull the probe out of the fluid and place it in my sump, the results change. I know what the salinity is in my system because I use a Tropic Marin Precision Hydrometer. It's dead accurate. The Neptune salinity probe is generally close, but only if I calibrate it to my 35.0 sump water.

 

[Art2249]

I tried and failed to calibrate mine 3 times. Finally let it air dry for 2 days first and success!

 

[madreefer11]

After years of bad readings, I finally had this thing calibrated. Trick is to take it out of the tank after calibration and put back in the calibration fluid and put back into the tank.

 

[salty_trout]

Wow this makes me want to stay away from Apex and I was just about to order one

My apex salinity meter Is always correct. I must be one of the lucky ones haha. Always agrees with my Milwaukee meter tho. I recommend getting an apex if you like less anxiety and stability... or some kind of controller. Not that you cant have perfection without them of course.

 

[Sleepydoc]

2. Rule out stray voltage and a possible device in the aquarium creating a noisy EMI environment. EMI is common with high-end DC pumps (think ABYZZ) or low end AC pumps. To determine the offending device, turn everything off in aquarium do the salinity number stabilize? If so, then turn one device on at time, starting with your return pump. Let it run for a minute or two, then take a look at your salinity readings. If you see your numbers become erratic, then the device you just turned on is either causing an EMI field or it has introduced some stray voltage into your tank. Moving the probe can help to mitigate the issue of EMI. With stray voltage, its typically recommended the offending device should be replaced. A grounding probe is a solution, but is really just a band-aide.

Below is a pic of my salinity probe graph with the light power graph superimposed on top of it. The light is a 6 bulb T5 fixture with an electronic ballast. It is plugged into the EB832 but the wires at least 12" away from the salinity probe cable. Pretty clear case of interference. This is a very common use scenario, so it's disappointing that Neptune doesn't have better shielding in place. Still, the variation is less than 1% which is plenty good enough for our purposes.

I calibrated my salinity probe when I first got my controller, got tired of messing with it and started ignoring it because it wasn't consistent. I haven't calibrated it since, as you can tell! Eventually, it settled out and as you can see it's pretty consistent except for the interference from the lights. What I realized, though, is that the salinity is probably the least important of the probes. What can affect it? The most common scenario is an ATO malfunction, but even if all 10 gallons of my ATO get dumped in at once, my SG would drop from 1.026 to 1.024. Not ideal, but not a catastrophe. The temperature is a far more important variable than the SG.