Even with all the confounding factors that this probe is susceptible to accounted for (bubbles, algae, detritus, electrical noise, etc), don't expect this thing to give you accurate or stable readings. The salinity in a decent size tank owned by anyone with a properly functioning ATO system doesn't change by more than 0.2 ppt from hour to hour, if that. Why then does this unit careen from, for example, 33.7 to 34.9 over the course of a day? Clean it, recalibrate it, reposition it, replace it with a new one, whatever, it'll keep doing this. Obviously the probe isn't measuring salinity. It measures conductivity. So either conductivity does not always equate with salinity (which makes the probe kind of useless for our purpose), the Apex probe design is flawed, or both.

When I first installed my PM2 mod with the salinity probe I was getting a reading of 35 to 40 in Fusion and I knew something was not right. So I contacted Neptune and their Superb customer service and they got right back to me about my issue. Anyhow, they told me to go ahead and shake the probes a few times since there could be air bubbles trapped up in the probe. Long story short, ones I gave the probe a little shake a few times, sure enough, the number shot straight up to 55. Word of advice, where ever you install your probes you have to make sure that there are not any air bubbles around them or you're going to be getting a false reading like I was. One of the best pcs for the Apex you can own b/c I don't know about you but I like to know approx where my salinity is at all times. Salinity probe a MUST & the PM2 MOD if you own a Apex..

Stopped working after about a year or so. Attempted to recal, but it didn't hold for long. Most of the time, shows 0. Not recommeded and I consider it an expensive mistake.

There are so many issues with the Neptune Apex, this uncalibrated salinity probe is just the tip of the iceberg. Why would you not include calibration solution in the box? It's finicky and you have to babysit the entire system, but what's worse is that we are now in 2017 with only a manual from the outdated 2014 edition. Customer service for anything Neptune sucks.

Stopped working after about a year or so. Attempted to recal, but it didn't hold for long. Most of the time, shows 0. Not recommeded and I consider it an expensive mistake.

In retrospect you really have to think about why you would want to spend over $200 on this after needing to buy the PM2 module, the probe and the calibration solution. The probe failed after 6 months and I am simply not willing to spend so much money on a prob.

At first it was sort of cool to see micro fluctuations in the salinity between ATO cycles (which are really irrelevant), but after that wore off it became pretty useless. Any notable fluctuations were always caused by the sensitivity of the probe. I was careful not to place it in an area where bubbles could stick to the probe, but I still had to shake it ever so often to get accurate readings. I wanted to use it as a fail safe, as a last resort if my ATO did not work properly. Due to it's unreliability the fail safe actually became the problem and the source of many false alarms. Eventually the probe die and read zero. Complete waste of money IMO. If you are looking for fail safe's, look at adding sanity checks using virtual outlets instead.

Works great, but can be a little stubborn when first put into water. Pay special attention to instructions and tips on how to remove air bubbles. You need to also have temp probe plugged into PM2 module for increased accuracy.

I just like a lot of people had a hard time cal. But did get it done. I think I had a hard time because the solution was cold. After cal. It works great. I used the pinpoint solution after I used the apex solution and it work fine. I have only been using it for a month,but have not had anything to complain about.

Had to standardize it a couple of times in the cal solution. Then had to tweak my tempt sensor a touch when I moved it over from the base module for temp compensation. Not really a big deal. Readings have been solid and dead on since initial setup. No complaints here.

This is a great add-on for anyone using an apex. I did find out that in order to keep my readings stable is was very necessary to add an addition temp probe to the PM2. At first I was getting crazy numbers and once I added the temp probe it has been spot on ever since.

Read the instruction and warning carefully. Avoid bubble, avoid others electrical equipment, and more importantly do not knock the probe on any hard surface. It is not hard to calibrate, but be sure to use calibration solution from Apex. I tried other brands, and the reading were off.

I've been running the probe for a little more than a month now, and overall it works as you expect. If you place it in an area of the sump or tank that does not have any bubbles, it is fairly stable and accurate. It does bounce around 0.1 ppt, so if the true salinity is 35, you will get values between 35.1 and 34.9, but this is within the spec of the probe.

I give it only 4 stars because the probe design makes it very susceptible to bubbles or detritus. I use a lot of different conductivity probes for work (i.e. YSI, hydrolab, seabird, etc), but none have this kind of problem. It is a poor design and I don't know why Neptune Systems uses it. You cannot place this probe in an area with bubbles unless you add some kind of protection against them.