**DISCLAIMER** I WORK FOR NEPTUNE SYSTEMS. I AM SHARING MY OWN PERSONAL EXPERIENCE AS A HOBBYIST WITH THE SALINITY PROBE, THEN PROVIDING SOME GUIDANCE ON ITS USE AND FUNCTION**
My probe works great. I haven't calibrated it in over 6 months, it matches my natural seawater refractometer all the time (and I calibrate the refractometer before every use). I have temperature compensation set to 2.4% and never see any affects of temperature on my probe.
The key to this probe is PLACEMENT. It needs some flow (so the water cannot be stagnant) and it cannot have any micro-bubble build up on it. For me, I mounted it in my return pump chamber on my Reefer 170. It is on the back side of my return pump and the probe is mounted at a slight angle to prevent any micro-bubble build up. This works for me. I have seen some people point a small power head (like a Koralia Nano 240) to provide flow and knock off any air bubbles that may accumulate on the probe.
The second thing I would mention is the probe is fragile. It breaks easily if dropped, knocked on the side of the sump ect. If you take the probe out of your sump and you hear anything in the probe rattling when you shake it, then it is broken and will cause erratic readings.
Here are some screen shots of my salinity probe graph and the probe mounted it my sump- nothing really all that special. I have graphed it against temperature and you can see the affects of temperature are fairly minor. In a period of a week my salinity has been 34.1 +/- .2 pr or so. That's a about 1.0256 to 1.0259 SG.
As I said, temperature only has a minor affect on my salinity measurements and I achieve this by using the temperature compensation feature used on the Apex. You can see I had a couple of colder days and my salinity was lower during that time, but not by much. I arrived at a 2.4% compensation factor after a period of a couple weeks of testing. I started with the 2.0% Neptune Systems recommendation, but was still seeing some pretty large affects of temperature on the probe over periods of couple days. I then moved it down to 1.8%, recalibrated and saw an even larger affect of temperature. So I went up to 2.2%, recalibrated and saw less of an affect but still enough to warranted some further adjusting. I went to 2.4%, recalibrated- got this behavior and was happy and left it alone.
Now, I'm not trying to say that some of you experience some real problems with your salinity probe and those aren't valid complaints. I hope just to illustrate here the probe works and can work very reliably. If you are experiencing issues with your probe I suggest the following:
1. Rule out that it isn't something in the tank. Place the probe in a cup of water for 10-15 minutes, do the numbers stay fairly stable? If so and the numbers are erratic in the tank, then you have stray voltage in the tank, EMI, but more likely air-bubble build up. If not, then see (4) below.
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.
3. If you see a slow and steady rise or fall of your salinity probe over a period of days, then that is the slow build up of micro-bubbles over time. Try finding another place in your tank, place the probe at an angle, point a small power ect.
4. If you take the probe out of water and just shake and you hear ANYTHING other than water draining out of the probe, then the probe is broken and needs to be replaced.
5 Make sure the probe is well seated into the Apex Base Unit. If it is not fully seated, then you can expect erratic readings.
All of the issues above cause erratic readings and deal with precision. Precision, in my opinion, in this case is the more important matter regarding this probe. The second part of the equation is ACCURACY. Inaccurate readings are typically due to errors or oversights in the calibration process. The process itself is really quite simple.
1. Place the calibration solution in tank to bring to tank temperature.
2. Set the temperature compensation value to 2.0% . (Here I have it set to 2.4%, which I detailed how I arrived at that above, this may not be the best TC for your aquarium).
3. I prefer a manual calibration, but that's just because at my heart I am a old school "Control Freak"
4. Take the probe out of water dry it- just give it a couple shakes.
5. Wait for the value to settle at the dry value and click OK
6. Open up the calibration solution and place the probe in the calibration solution. Leave the solution in the water during the calibration
7. Hold the bag at a 30-45 degree angle in the water with the probe angled as well
8. Give the probe a couple twirls in the bag and maybe a tap or two. This releases any air bubbles that may be on the probe.
9. Let the probe sit for a bit and settle.
10. Select OK after you don't see the settling number change with +/-2 units for 10 seconds. Really if there are not any air bubbles and the solution is staying the same temperature as the tank water, then this shouldn't take more than 30-45 seconds to settle.
11. After calibration the probe should read 34.9-35.1. Those numbers indicate an accurate calibration. If you don't get those measurements in the solution, then the calibration was not accurate.
Reading over this post, its pretty long-winded, but I hope it helped provide some details of how the probe can work reliably. I encourage you to contact our support team if you are having trouble with you salinity measurements after following some of the tips here.
Thanks for all your feedback everyone. It is appreciated.
- Paul
