Is the salinity probe worth it?

[BigHildy53]

My Apex salinity probe calibrates, but does not read correctly. It reads a 40 ptt, but a refractor and digital salinity meter both read 1.025. Before replacing, I was wondering if it worth the money. The salinity is easily checked separately.

Thoughts?

 

[rich nyc]

I have the same problem but it sort of gives me an idea of where it is

 

[Dom]

What is the tank temp?

 

[CNDReef]

Make a small batch of water at 30 ppt and see what the probe reads. If it reads 35 ppt you can calculate its off by -5 ppt.

 

[BigHildy53]

What is the tank temp?

Apex 78.3, separate nist thermometer 76.8.

 

[Muttley000]

I run two Neptune salinity probes, one in my sump and one for my mixing station. They are a little finicky to calibrate. When mine reads off I usually shake a few bubbles out of it and I am good to go again.

 

[miPapareef]

To answer your question directly, I would never replace mine if it stopped working. Because I have a digital refractometer to mix new salt water, I also use it measure the tank every few days. It’s way more accurate and it’s the best way to match the water change water to the tank.

Here’s a graph of how my apex probe goes off the rails every few months. I think it’s due to a sponge or algae getting on the tip. I dip and swirl it in a cup of RODI when this happens. The other thing I’ve found to help with the accuracy of the reading is to only have the bottom 1.5 inches of the probe under the water. If I put 4” of the probe under water the reading is higher.

Also when you calibrate the probe, have the wiring and probe as close to the final installed location as possible and make sure the calibration fluid is at the same temp as the tank water. Also have a grounding probe in the tank and keep all other wiring away. But the bad news is even when I do all that the probe measurement is still very noisy as you can see from the last graph.

 

[n2585722]

Conductivity probes measure the conductivity of water between the probe tips. If anything gets between these tips it will cause a incorrect reading. This includes snails pods etc in your tank or air bubbles. You can try placing it in a high flow area where there is less likely to be snails, pods or air bubbles at. Try and change the location around and see if that helps. If it is consistantly off and you are sure of you tanks salinity then use you tank as one of the cal points when calibrating instead of cal solution. I don't have an Apex, but I do have a controller with a salinity probe and this appear to be an issue with all of them.

 

[BigHildy53]

Conductivity probes measure the conductivity of water between the probe tips. If anything gets between these tips it will cause a incorrect reading. This includes snails pods etc in your tank or air bubbles. You can try placing it in a high flow area where there is less likely to be snails, pods or air bubbles at. Try and change the location around and see if that helps. If it is consistantly off and you are sure of you tanks salinity then use you tank as one of the cal points when calibrating instead of cal solution. I don't have an Apex, but I do have a controller with a salinity probe and this appear to be an issue with all of them.

I have cleaned the tips, with general cleaning solution probes, and soaked in storage solution to ensure the tips are hydrated. I've had it for about a year. I think I'll stick with manual readings.

 

[Waters]

I don't worry as much about the actual number, as I do changes in that number. As long as it stays consistent, and you know the correct reading, it is worth using......strictly as a safety if your ATO malfunctions and dumps a bunch of fresh water into the tank. You can shut that outlet off based on the salinity dropping.

 

[Breadman03]

I once had the cable to my breakout box get disconnected on day 1 of a 15 day vacation. I reprogrammed my Apex to run my topoff based on the salinity reading and it kept my water level right where I wanted it.

 

[Flexin]

Not worth it..

 

[Sleepydoc]

I don't worry as much about the actual number, as I do changes in that number. As long as it stays consistent, and you know the correct reading, it is worth using......strictly as a safety if your ATO malfunctions and dumps a bunch of fresh water into the tank. You can shut that outlet off based on the salinity dropping.

This.
The salinity probe is the least reliable of the Apex probes, IME/IMO. (I’ve read that they are problematic with other controllers, too, so it seems like it’s not just Apex.)

As others have mentioned, they are susceptible to micro bubbles. Mounting the probe at an angle and mounting it in a place that doesn’t see a lot of bubbles can help. I’ve also read that electrical interference can cause issues, so how you have the cord for the probe routed can play into it as well. For whatever reason, I found that my probe has gotten better as things settled in. I just checked and over the last 2 days it’s only varied between 45 and 45.4.

 

[rkpetersen]

I’ve also read that electrical interference can cause issues, so how you have the cord for the probe routed can play into it as well.

I can confirm that this is absolutely a real effect. If you have high current wires in close proximity to the probe cable, you may get elevated conductivity/salinity measurements. The graph below is from a system of mine that had two heaters alternating duty, but often working in tandem at night. The heater cords and probe cable ran together for only a short distance, through a bottleneck. Nonetheless, it was sufficient to alter the salinity reading substantially when both heaters were on.

This second graph shows the relationship between the salinity reading, total power consumption, and the duty cycles of both heaters.

 

[Biglurr54]

Mine is off after many calibrations. that being said it does give you an idea of whats going on. It hovers right at 36ppt even though the tank is at 35ppt. It gives me an idea and it does drift .2 in either direction. I use it as a baseline. If i see a major swing in the numbers then I make sure everything is alright. Last night i did a 25% water change and the salinity dropped to 34ppt. i was nervous that something was wrong so i grabbed my spare refractometer and calibrated it and tested against my main refractometer. Everything was spot on at 35ppt. I wiggled the probe, bubbles came out, and we are reading at a steady 35.4 ppt on the probe now.

Its not reliable and its not a necessity, but if it catches my salinity creeping up, or catches a stuck on ATO, even just once, then I am a happy camper and it was worth it. It will never replace manual salinity monitoring which I do every other day, but it sure is nice to log onto fusion at my desk at work and see that salinity sitting where it is supposed to be.

 

[roberthu526]

Salinity probe is pretty much trash. I have calibrated mine many times and I finally got tired of it and just leave it be. If I trusted my water with the probe I wouldn’t be in this hobby anymore. The reading is usually way off.

 

[GK3]

It sounds like most of the people who are against the salinity probe are due to calibration difficulties and/or reading different from refractometer.

Realize that a salinity probe is measuring conductivity while a refractometer is a direct measure of the salt content. There are a number of factors that must be controlled the make them read absolutely identical, primarily temperature. I usuallly find that it’s best to calibrate my salinity probe then measure with a refractometer. The refract will say 1.025 and let’s say my probe is measuring 34.1. I now know my probe should be around 34.1 for my levels.

If you are calibrating your probe and at the end getting something like 23.2 or 97.6 when you know you water is at 1.025, then I’d say the calibration was bad. In calibrating mine, here are things I’ve noticed:

1. I float the calibration solution to bring them to tank temp.
2. When I put the probe in the solution I move it around almost shaking it to knock off air bubbles.
3. Make sure when you stick it all the way into the bad, the probe isn’t touching the side of the bag.
4. Make sure the probe stays clean. Cleaning the tips should be part of regular maintenance.

As far as differences when there are electrical devices on or off, this has to be coming from the cable. pH and salinity probes are susceptible to electrical interference from stray voltage in the water, like from a pump. But the apex uses galvonic (I believe that is the correct wording) to eliminate this. You can read about it on their website. So the only way to pick this voltage up should be in the cable between the probe and the unit. However those cables are shielded so I’d suspect it would take a high amount of voltage or current to interfere that significantly.

 

[ca1ore]

I do use the apex salinity probe, and find it generally useful. It is twitchy and finicky, even though I have it in a spot where any 'contaminants' should be at a minimum. It's helpful to me as a continuous monitor and alerts me if something changes. I would NEVER use it to control anything - just asking for trouble. Just in the last few days mine has been bouncing around between 32 and 37 yet a refractometer check yields 1.026. Not sure why. Probe is only 5 months old.

 

[roberthu526]

It sounds like most of the people who are against the salinity probe are due to calibration difficulties and/or reading different from refractometer.

Realize that a salinity probe is measuring conductivity while a refractometer is a direct measure of the salt content. There are a number of factors that must be controlled the make them read absolutely identical, primarily temperature. I usuallly find that it’s best to calibrate my salinity probe then measure with a refractometer. The refract will say 1.025 and let’s say my probe is measuring 34.1. I now know my probe should be around 34.1 for my levels.

If you are calibrating your probe and at the end getting something like 23.2 or 97.6 when you know you water is at 1.025, then I’d say the calibration was bad. In calibrating mine, here are things I’ve noticed:

1. I float the calibration solution to bring them to tank temp.
2. When I put the probe in the solution I move it around almost shaking it to knock off air bubbles.
3. Make sure when you stick it all the way into the bad, the probe isn’t touching the side of the bag.
4. Make sure the probe stays clean. Cleaning the tips should be part of regular maintenance.

As far as differences when there are electrical devices on or off, this has to be coming from the cable. pH and salinity probes are susceptible to electrical interference from stray voltage in the water, like from a pump. But the apex uses galvonic (I believe that is the correct wording) to eliminate this. You can read about it on their website. So the only way to pick this voltage up should be in the cable between the probe and the unit. However those cables are shielded so I’d suspect it would take a high amount of voltage or current to interfere that significantly.

The problem is a couple of weeks after calibration it falls from 34.9 to 32 then 31. I understand that it is going to fluctuate a bit in the long run but a couple of weeks is just too short...

 

[Randy Holmes-Farley Verified Community Expert]

Realize that a salinity probe is measuring conductivity while a refractometer is a direct measure of the salt content.

I have to disagree with that particular claim. Using a refractometer to measure changes in the speed of light traveling through the solution due to the presence of salts is no more direct than using a conductivity meter to measure the movement of salt ions in an electric field. The only direct method is drying and weighing, but that's actually not as accurate as either refractive index or conductivity.

I don't disagree that the controllers have poorly implemented conductivity measurement, and stand alone units do a far better job (IMO). I have used and very much like the Orion model 128 with a four electrode probe on it, but it is very expensive, at least when new. I have also used an like the Pinpoint, but it is slower to respond, presumably due to slower temperature equilibration.