Salinity probes...what's the story here? Why aren't they reliable?

[Daniel@R2R]

I love my Hanna salinity tester. I have found it to be really reliable, but sometimes I really wish that monitoring salinity could be as easy as using a salinity probe (a la tank temperature and pH). However, IME (and it seems I'm not the oddball) salinity probes just aren't that reliable. What is it that makes this an issue? What could be done to have a more reliable way to monitor salinity?

Photo credit: @aquaman3680

 

[Gtinnel]

I have the same Hanna salinity tester and hate it. I mostly go by my apex probe and it is generally reliable for me, but every once in a while I will get a crazy reading. I’ve always heard it was because of air bubbles but I don’t actually know that to be true.

 

[BanjoBandito]

I think temp can have adverse effects because they use a electrical current to test ions or something like that. Good ones have automatic temperature compensation built in. A refractometer works via light sensors, much more reliable. Also a lot depends on the condition of the actual probe.

 

[Sean Clark]

I will echo the dislike of the Hanna Salinity Checker. It drifts a lot and very quickly in my experience.
I prefer the digital refractometers.

@eag Has a fantastic thread on the Apex salinity probe stability here:

(Almost) Everything You Need to Know About Apex Salinity Calibration and TC Factor

I was trying to calibrate my new salinity probe a few weeks ago, and ran into all sorts of problems. Calibrations that were way off the mark, big fluctuations in readings that couldn't possibly be correct (and were verifiably not), etc. After searching around the internet, it was clear that a...

www.reef2reef.com

 

[HuduVudu]

They all suck and I finally went old school and got a hydrometer that floats. This helps me compensate for the crappy meters, because I have a known baseline to work from.

 

[TheWB]

They all suck and I finally went old school and got a hydrometer that floats. This helps me compensate for the crappy meters, because I have a known baseline to work from.

I have one of those as well. Hate the Hanna for reasons others above listed. My apex salinity probe actually works pretty well but the floating hydrometer allows a quick, accurate spot check.

 

[HuduVudu]

I have one of those as well. Hate the Hanna for reasons others above listed. My apex salinity probe actually works pretty well but the floating hydrometer allows a quick, accurate spot check.

I am thinking about going back to the swing arms and using the floating hydrometer to calibrate that.

I can't believe with all of the tech that this hobby has seen how little of it actually works.

This is sad to me because the tech could really help instead we get rushed garbage designed to empty the pockets of new hobbyists. I guess when the real rain comes then we will start to see a return to products that actually help people and advance the hobby.

::sigh:: Rant off.

 

[Dennis Cartier]

Salinity probes can be very difficult to use. They are very sensitive to temperature, and the probe type, Apex, Atlas Scientific, do not include automatic temperature compensation. This causes them to drift with temperature changes if not provided with an accurate external temperature reference.

I am currently running a test on my frag tank for an automatic salinity management system I created using Atlas Scientific EC probes. Basically what they warn you not to do, depending on an EC probe for your salinity.

To be confident in the system, I run 3 Atlas Scientific EC probes at all times, and compare all 3 to detect any probe that has become impacted or invalid. I have found that keeping a steady stream of water flowing past them helps greatly keeping them accurate.

As long as i have a quorum of 2 of the 3 probes passing sanity checks, I use the reading to drive an ATO function.

This type of management would have great application for 2 part dosing as well. Instead of a water level sensor controlling the ATO, a high water level reading would trigger a pump to waste, and the low water level reading would trigger the addition of new saltwater.

The other feature that I think is neat, is that if you have a continuous water change that uses a dual headed pump, and the flow rates get out of sync, a situation that has bit me a couple of times in the past, using real-time salinity management corrects it automatically before it causes an issue for your tank.

For safety, I have a benchtop Thermo Scientific Orion Conductivity meter running at all times for manual cross checks. I also use a Tropic Marin high precision hydrometer to calibrate the system.

The only thing I don't like is the cost of EC probes. They are more expensive than pH and ORP probes, as are their interface hardware.

 

[Rob K]

For me, the floating hydrometer is quick and accurate. I do have a Hannah salinity tester, but find it’s just as easy and quick to use the hydrometer.

 

[Garf]

We use conductive probes at work a t 11mS, 50 and 40us. They need monthly calibration.

 

[Randy Holmes-Farley]

I love my Hanna salinity tester. I have found it to be really reliable, but sometimes I really wish that monitoring salinity could be as easy as using a salinity probe (a la tank temperature and pH). However, IME (and it seems I'm not the oddball) salinity probes just aren't that reliable. What is it that makes this an issue? What could be done to have a more reliable way to monitor salinity?

Photo credit: @aquaman3680

I don't know exactly what the issue with cheap ones is, but with high quality conductivity probes, it is definitely as simple as measuring temp and pH (in fact, the best ones do measure and report temperature). There are features of better probes missing on cheap ones (like 4 electrodes vs 2 to reduce certain effects), but I'm not sure which attributes(s) cause the most issues for reefers.

I also think leaving a conductivity probe in the water 24/7 is not ideal since accumulating stuff on it can lower the detected conductivity, but that's obviously not the problem with the Hanna.

Conductivity probes implemented by reef controllers also have special issues. One of these may relate to temperature measurement and correction. All conductivity meters self correct for temperature changes, but controllers are measuring temperature in different locations and some folks may not understand this when they calibrate. Some also can have the temp correction altered or turned off, neither of which makes sense for a dedicated reef controller.

 

[Randy Holmes-Farley]

I think temp can have adverse effects because they use a electrical current to test ions or something like that. Good ones have automatic temperature compensation built in. A refractometer works via light sensors, much more reliable. Also a lot depends on the condition of the actual probe.

All of refractometers and conductivity meters and floating glass hydrometers need temperature corrections. SOme may just not be implemented properly or in a user friendly way. I noticed that my Pinpoint takes much longer to come to temp equilibrium and give a final value than my Orion (high end meter and probe). They get to the same point, but not at the same rate.

Refractometers are not more reliable than high quality conductivity meters. Chemical oceanographers use conductivity meters, not refractometers. The modern salinity scale (PSU) is actually defined by a certain conductivity equally 35 ppt.

 

[BanjoBandito]

All of refractometers and conductivity meters and floating glass hydrometers need temperature corrections. SOme may just not be implemented properly or in a user friendly way. I noticed that my Pinpoint takes much longer to come to temp equilibrium and give a final value than my Orion (high end meter and probe). They get to the same point, but not at the same rate.

Refractometers are not more reliable than high quality conductivity meters. Chemical oceanographers use conductivity meters, not refractometers. The modern salinity scale (PSU) is actually defined by a certain conductivity equally 35 ppt.

I stand corrected. Thanks for not taking a victory lap on me. lol.

 

[Dennis Cartier]

I also think leaving a conductivity probe in the water 24/7 is not ideal since accumulating stuff on it can lower the detected conductivity, but that's obviously not the problem with the Hanna.

I saw that issue with the Atlas Scientific probes. For the first 10 days or so after being placed in tank, the reading would keep increasing and then eventually plateau after what I surmised was a film being built up on the conductivity cell. At that point, they would then float and drift about, and would sometimes have abrupt swings as the local invertebrates would squat in the conductivity cell hole of the probes.

The floating and swings was easy to detect when comparing 3 probes to each other in real time. My solution was to place each probe into a 'in sump manifold' that would keep water flowing past the probes to normalize the films and keep the squatters moving on. That one change removed the majority of the issues for me.

I did try installing the probes in an external 'normal' manifold type of arrangement in existing plumbing. That was my first choice for the installation in fact. However I had a head scratching issue where they would not work across the whole range of the temperature swing of the tank using that arrangement. I could not figure it out, and then a fortuitous bug in my code where I accidentally had the temperature compensation reading being pulled from a hardcoded manifold temperature reading instead of the water temperature and the issue (almost) vanished. After investigating, I concluded that the probes were being impacted by the temperature of the manifold, which was being impacted by the room air temperature. That is not stable or sustainable situation as the room temperature can and will vary seasonally, where the water temperature should stay in a narrow band. The in tank manifold was the solution.

 

[JCOLE]

I love my Hanna salinity tester. I have found it to be really reliable, but sometimes I really wish that monitoring salinity could be as easy as using a salinity probe (a la tank temperature and pH). However, IME (and it seems I'm not the oddball) salinity probes just aren't that reliable. What is it that makes this an issue? What could be done to have a more reliable way to monitor salinity?

Photo credit: @aquaman3680

I agree. I have had great results with the Hanna meter but my Apex salinity probe is all over the place.

Have you heard of the SPS? It's a salinity probe stability kit. It sends water through it constantly eliminating bubbles, etc. I have one on hand and plan on installing it this weekend. I will update afterwards. Seems promising though.

Salinity Probe Stability Kit (SPS)

Monitoring salinity in an aquarium can be a challenge-- small bubbles and debris can interfere with your conductivity probe, leading to inconsistent and unreliable results.Vivid Creative Aquatics has tackled this problem head on with their Salinity Probe Stability Kit. The "SPS" Kit is carefully...

www.bulkreefsupply.com

 

[piranhaman00]

VerGee refractometer calibrated with RODI (not a reference standard) for me

 

[fryman]

The neptune salinity probes are notoriusly unreliable but I think I've now got mine dialed in.

Biggest issue seems to be noise, which can be addressed with placement (avoid other probes or wires) but better yet is to use a clip-on ferrite ring like so:
(Pack of 20pcs) Clip-on Ferrite Ring Core RFI EMI Noise Suppressor Cable Clip for 3mm/ 5mm/ 7mm/ 9mm/ 13mm Diameter Cable, Black


I also placed it in good flow, clean monthly in citric acid, and re-verify calibration after each cleaning.

 

[atomos]

I have the same Hanna salinity tester and hate it. I mostly go by my apex probe and it is generally reliable for me, but every once in a while I will get a crazy reading. I’ve always heard it was because of air bubbles but I don’t actually know that to be true.

In my case recently, it was the sensors. was told to get cardboard (kraft brown) and to vigorously rub the sensors. after a few tries (4 tries), the tester calibrated and tested fine until two days ago----now it's back to the same spot. hoping hanna CS will have other pointers since the cardboard fix didn't work this time

 

[Ceti]

Salinity probes can be very difficult to use. They are very sensitive to temperature, and the probe type, Apex, Atlas Scientific, do not include automatic temperature compensation. This causes them to drift with temperature changes if not provided with an accurate external temperature reference.

I am currently running a test on my frag tank for an automatic salinity management system I created using Atlas Scientific EC probes. Basically what they warn you not to do, depending on an EC probe for your salinity.

To be confident in the system, I run 3 Atlas Scientific EC probes at all times, and compare all 3 to detect any probe that has become impacted or invalid. I have found that keeping a steady stream of water flowing past them helps greatly keeping them accurate.

As long as i have a quorum of 2 of the 3 probes passing sanity checks, I use the reading to drive an ATO function.

This type of management would have great application for 2 part dosing as well. Instead of a water level sensor controlling the ATO, a high water level reading would trigger a pump to waste, and the low water level reading would trigger the addition of new saltwater.

The other feature that I think is neat, is that if you have a continuous water change that uses a dual headed pump, and the flow rates get out of sync, a situation that has bit me a couple of times in the past, using real-time salinity management corrects it automatically before it causes an issue for your tank.

For safety, I have a benchtop Thermo Scientific Orion Conductivity meter running at all times for manual cross checks. I also use a Tropic Marin high precision hydrometer to calibrate the system.

The only thing I don't like is the cost of EC probes. They are more expensive than pH and ORP probes, as are their interface hardware.

It all reads very impressively!! Can you share some pics? Maybe a YouTube video?

 

[Dennis Cartier]

It all reads very impressively!! Can you share some pics? Maybe a YouTube video?

It's not really ready to be photographed currently. I have it running with a messy install on my frag tank for testing. I plan to use it on my 500G build, so it will appear in my build thread once I get the tank running (hopefully later this summer).

This is the thread where I was developing the system (though it's mostly about verifying the hardware changes since I last used these ones).

Opinions on current Atlas Scientific hardware

Hey reef-Pi users. I am considering purchasing a bunch of Atlas Scientific boards for a custom build I have underway (non Reef-Pi). I have used the Atlas Scientific stuff in the past, but it was before they had electrical isolation support built in, and the results were fairly terrible at that...

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