salinity probe reading wrong

[Eand]

This is provably an old thread but i just wanted to say that i haven't been able to calibrate the salinity probe but since my fluctuates from 58 -61 conductivity and the refractometer reads 1.026 - 1.028 i just decided to just monitor fluctuations between the two numbers and not worried about where the probe should be if calibrated. Trident should come up with a fix to this problems soon anyway. I hope.

[dmaister]

Since the thread was recently reopened, I wanted to share this anecdote, based on Diznaster's previous comments about stray voltage. Maybe this will help someone in the future. I've only had my Apex up for less than a month, and when I first setup the salinity probe, and I had weird swings even after calibrating (between 13 and 40 something). I reached out to support and they helped me get it manually calibrated. It has been running fairly stable for a few weeks.

As I'm still cycling and wanted to introduce coralline algae at a recommended 78-82 degrees, I added an old adjustable heater in the display tank (connected to the EB832) to raise the temp to 80 (my main heaters are preset to 78 and run about 77.6). As I did that, I noticed the salinity measurement following the temp measurement (see chart) and ORP doing the opposite.

Screen Shot 2022-03-18 at 12.44.32 PM.png

Since I also started dosing All-for-reef to get PH/Alk back up for the coralline, I wasn't sure whether the salinity was increasing due to that - it shouldn't have. But it was just coincidental that salinity probe went up. I have a ground probe and double-checked the S.G and PPT with a Milwaukee refractometer and it looked fine (1.025 / 34 PPM).

That's when I found this thread and reading about stray voltage connected some dots.

I currently have the heater in the DT, but have stopped the return pump to "break" the water circuit between the salinity probe and the DT for a few hours to see if anything changes in the sump parameters (I know, not exactly scientific, but...). I will disconnect the old heater (once I get a newer adjustable one) and see if it changes the salinity reading. But if the salinity inconsistency is connected to the introduction of the old heater - that is definitely interesting. I may also try connecting the heater to a different outlet nearby - but they are all on the same circuit - so not sure that make any difference. But it goes to show how different types of equipment in different systems may cause sensitivity in how these tools measure the parameters.

I will post back here with the testing results after a few hours / days.

[edmcnierney]

I'm an Apex newbie so I figured I'd start by contributing some info before I ask for some!

I'm setting up a new tank and had a frustrating time getting my salinity probe to work. At first it read absurdly low numbers, then I did an automatic calibration and they looked reasonable. I couldn't find my old refractometer so I had no other reference. I added salt until it came up to the low 30s. I belatedly realized that I was not bringing the calibration solution up to tank temperature. My tank is on the first floor but the sump is below it in the basement of a 200-year-old house. It's 58 degrees down there. So I recalibrated correctly and still got a number below 35.

After adding a little more than a 55-pound bag I realized I had to be adding way too much salt. I managed to find my old refractometer and I was at 45 ppt! I recalibrated again and still got a number below 35.

I had a very helpful support call with Carlos, who very clearly knew what he was talking about. After poking around for a while he told me that the probe's operating range is only up to 40 ppt and that it will give unreliable results above that. He told me to get it down below 40 and check again. I was a little skeptical but gave it a try and it worked. The probe is now working as expected and matches my refractometer. Of course, it's a little amusing to be told that to correctly measure my salinity I needed to get my salinity within the right range. I didn't see a mention of this "over 40 ppt" issue earlier so I thought I'd add it to the list.

Bottom line: you can get a cheap refractometer for under $20 or even a swing-arm one for less than $10. Get one if you don't have one already. They may not be very precise, but they're unlikely to be grossly inaccurate.

[dmaister]

I will post back here with the testing results after a few hours / days.

So letting my heater run a few more days, there was some slight change when I broke the water loop between the display tank where the heater was temporarily located and the sump, which tells me there is definitely a connection to the addition of the heater. I need to test the theory once more - but hadn't had a chance since last week. Just posting the image here to follow-up on my previous message.

I confirmed the salinity was at 1.025-1.026 / 33-34 with a Milwaukee - so it wasn't actually changing as the probe was indicating.

Whether it's just a bad heater, or whether it needs temperature recalibration - I'm waiting to hear from support - as Ed said - they are very helpful.

Screen Shot 2022-03-23 at 5.37.52 PM.png

[zombie]

Dmaister, you need to enable temp compensation. Conductivity increases by somewhere between 2-2.6% for every degree C increase. Temp compensation cancels out this change so conductivity stays stable.

Your variation looks to be on the high side of that range, so start with 2.6 and tune from there.

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