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

[Saltyanimals]

Great guide!
I followed it thoroughly with my new (and first) salinity probe, yet these are the results after a week
From 37 ppt down to 30.6. My real salinity is stable at 35.

Very disappointing, and not sure what to do..?

Since this is your "new and first" salinity probe, I would just give it time to settle down and not reaction or take action just yet. I would manually check the salinity i.e refract for now and give your probe several weeks to settle in.

It has been said that probes may develop basic biofilm which "breaks it in" so to speak. I've seen this with pH probes and lots of readings here where folks allow their new probes to sit in tank for weeks before trying to calibrate. I would assume it may apply here as well.

However on the flip side, my salt probe is 5-8 years old and still kicking. I noticed it will get an occasional finicky where I see a drastic drop in readings with no changes to the tank. This is clearly a probe issue and it seems to resolve itself in days. Sometimes I give it a few good taps to make sure I don't have air pockets somewhere on it that may affect the reading.

 

[keithIHS]

Like Saltyanimas, if I see mine drifting down, I give a couple of taps to make sure there aren't any bubbles inside (it's mounted pointing upward at a 45-80 degree angle). I also mounted it in a location that is away from the fuge light in an area that doesn't have many bubbles. If the taps don't do it, I'll give it a couple of quick dunks in and out of the water to dislodge anything that's inside followed by taps to dislodge bubbles. Every few months I'll carefully run a flat toothpick around inside to dislodge anything that might be inside, followed by dunks, followed by taps (while pointing upward).

 

[All_talk]

I don't seem to have an issue with bubbles. My probe is in the same section of my sump as my drain and skimmer, lots of bubbles large and small, but also lots of flow.

My readings really tuned in well after I calibrated it to the tank, no offset and less variation (graph 1). I recently removed some water while adding coral which the ATO backfilled, and then later I corrected the salinity which the probe tracked well (graph 3). It has agreed with my refractometer which I calibrate with a precision hydrometer. I pretty happy with it at this point.

 

[Saltyanimals]

I simply moved my probe holder about 10 inches over as part of my sump cleaning and it immediately reflected a bad reading. This is of course impossible give it was "correct" just a few minutes earlier. I gave it the usual taps to dislodge bubbles to no avail. I ran out of time so decided to fix it later. Several more taps and movements the next day and finally it's back to my expected range. Went from 34.x down to 30.x back up to 45.x + all over the last 2 days.
Funny graph: Notice the far left and far right. Right back to where I was on the rollercoaster.

Summary? Imagine if this was a new probe into an unknown tank salinity. I would be banging my head against a wall trying to understand why my new probe is wrong spending countless calibration bags trying to get it right. This is a good example of knowing where your salt really is before installing a new probe which may lead you to take unnecessary and/or lethal action to your tank.

 

[All_talk]

I simply moved my probe holder about 10 inches over as part of my sump cleaning and it immediately reflected a bad reading. This is of course impossible give it was "correct" just a few minutes earlier. I gave it the usual taps to dislodge bubbles to no avail. I ran out of time so decided to fix it later. Several more taps and movements the next day and finally it's back to my expected range. Went from 34.x down to 30.x back up to 45.x + all over the last 2 days.
Funny graph: Notice the far left and far right. Right back to where I was on the rollercoaster.

Summary? Imagine if this was a new probe into an unknown tank salinity. I would be banging my head against a wall trying to understand why my new probe is wrong spending countless calibration bags trying to get it right. This is a good example of knowing where your salt really is before installing a new probe which may lead you to take unnecessary and/or lethal action to your tank.

Agreed, I like seeing the graph in Fusion but if it goes screwy it doesn't mean take action, it just mean to check things out.

 

[DeputyDog95]

Not sure what's going on... My old probe was falling apart, so I just replaced it about a month or so ago. Can't get the darn thing to calibrate. It's usually pretty easy. Take it out, wipe it off, calibrate dry, stick it in the tank, calibrate wet, 35ppt at my typical tank temp of 79. I have the TC factor set to only point one so it barely does anything. Now I can't get it to read over 34.3, despite telling it that it's in a 35ppt solution (my tank water).

Any suggestions to force it to read 35ppt as the current baseline?

 

[All_talk]

Bumping this thread up because its a very good one, and for a little advice.

Since setting up temp correcting and calibrating to the tank water my salinity probe has been very stable and accurate. But recently I had a issue with one of my heaters which lead to more temp variation than normal and I noticed my salinity probe has a small opposite reaction to temperature, i.e. salinity reads lower when temps go higher (see included graph). I suspect this means my TC factor could be better tuned. Currently its at 1.9, does it need to be increased or decreased? I guess I can experiment a little and figure it out, just figured it would be worth asking to see if anybody had experience.

Certainly, the system is working well enough but I like to fine tune things if I can.

 

[Righteous]

Bumping this thread up because its a very good one, and for a little advice.

Since setting up temp correcting and calibrating to the tank water my salinity probe has been very stable and accurate. But recently I had a issue with one of my heaters which lead to more temp variation than normal and I noticed my salinity probe has a small opposite reaction to temperature, i.e. salinity reads lower when temps go higher (see included graph). I suspect this means my TC factor could be better tuned. Currently its at 1.9, does it need to be increased or decreased? I guess I can experiment a little and figure it out, just figured it would be worth asking to see if anybody had experience.

Certainly, the system is working well enough but I like to fine tune things if I can.

I believe the recommendation for TC is around 2.1-2.2. I have mine set at 2.2 and it works great.

By the way, no need to recalibrate the probe if you change TC, as long as it was calibrated with a TC above 0.

 

[DeputyDog95]

Bumping this thread up because its a very good one, and for a little advice.

Since setting up temp correcting and calibrating to the tank water my salinity probe has been very stable and accurate. But recently I had a issue with one of my heaters which lead to more temp variation than normal and I noticed my salinity probe has a small opposite reaction to temperature, i.e. salinity reads lower when temps go higher (see included graph). I suspect this means my TC factor could be better tuned. Currently its at 1.9, does it need to be increased or decreased? I guess I can experiment a little and figure it out, just figured it would be worth asking to see if anybody had experience.

Certainly, the system is working well enough but I like to fine tune things if I can.

This probably more info than you were asking for, but figured I would share anyway

If I remember correctly, the more you increase the TC, the more it decreases the salinity reading.

That being said, since I started calibrating to tank water using my Hanna conductivity meter as the reference point, and the Neptune salinity probe has been great. I had like 4 different salinity devices and the Hanna, despite being simple, inexpensive, and easy to use/calibrate, was always the closest to my ICP tests. After testing a couple of times, I stopped using all my other salinity devices (manual refractometer, Milwaukee digital refractometer, etc) and have stuck with the Hanna.

I am fastidious about maintenance on it though. I keep it stored in it's case, I rinse with RODI water every time and dry it before putting it back in the case, and I calibrate it pretty frequently (at least every 60 days). It's easy and takes about a minute.

Another bonus for using the Hanna... I mix my water change water to a specific lower salinity to account for salinity creep because I dose around 100ml a day of sodium based alkalinity and want to keep it at 35ppt. Otherwise, the salinity goes up quite a bit (min half a point) even after just a couple of months. I use one of the wizards online to tell me what to mix the salt to based on my current salinity reading, the volume of water in the system, and the amount of the water change water. From there, I add 2000g of salt to my mixing barrel, let it mix clear, measure it, and then slowly add the salt while measure it in real time as it goes up with the Hanna device floating in the water. Makes it super easy to make up custom salinity batches of water. It's basically a real-time probe in your mixing barrel.

For me, my tank temp variance is less than half a degree a day... So I have the TC turned to it's minimum. Which is .1 if I remember correctly? Basically, it's borderline turned off and I only have it on the min so I can play it with it a little without having to recalibrate. That being said, I find I almost never monkey with it anymore and if I start to get a little drift with the Neptune probe, usually sliding it up and down in the probe holder a few times will clear any debris or air and get it back to the correct reading.

See attached screenshot from this morning. My AC is being serviced this morning as it's not working as well as it should, or the tank never usually goes over 79. But the office is getting a hotter than usual now and the GHL cooling fans are struggling to keep up.

So if your tank temp rarely deviates, I would just leave the TC off, or close to off, as it gives wider readings with it on in my experience. Now if you're swinging a few degrees a day, that's probably a different story. If you get your heater straightened out and your temp settles to fairly tight margins, I would run it the way I am.

 

[All_talk]

Follow up...

My tank typically runs with less than 1 degree change, but in the summer it may heat up a little on a hot afternoon (no central AC). I would like the TC to be tuned so that salinity reads correct if the temp is outside normal.

I tried running the TC at 2.2 and its seemed worse, now its 1.7 and seems better. With my heater issue sorted, I have had to force some slight temp swings to test things, but its looking like slightly lower than the 1.9 I was running will tune it in.

 

[Bramzor]

Use Manual calibration and figure out what your dry and wet value is supposed to be. If you know that, you can watch it during next calibration and see what happens. My dry and wet values are 68 and 484.
So I know that when these are off during calibration, it’s probably bubbles or a bug in Apex. Noticed that in some occasions that you click next too quickly during manual calibration, dry value will read 0 or -5 and does not correct. If I go slow, it measures 68 consistently (after RO rinse or x hours dryout). If I do not rinse or wait it to dry out, it will drop from 72 to 68. This will only affect the lower portion of your salinity reading so if you want a bit higher resolution, it’s better to not rinse it or let it dry out. You do need to tap it a little bit. Everything above 80 it’s probably still reading a wet value, even if it’s out of the tank.