Salinty Peaks When Lights Go Out

I've never been able to get accurate readings out of my probe. I've re calibrated many times using the appropriate steps and it always ends up high. It's mostly accurate during the day but at night it's at least 1.5 PPT too high. It seems like it's starts going up about 30 minutes after the lights go out and goes down when the lights come on. Any ideas? I've played with temperature compensation and nothing really changes it. I'm using the 2016 Apex with Kessil 360WE lights. I have the lights on a separate power bar. I always compare against a carefully calibrated VEE GEE refractometer which always reads around 35 PPT.

Make sure the kessil cable isn't parallel to the probe wire. More than likely it's induced current/voltage on the probe wire.

You might be an engineer if...You have no life and can prove it mathematically.

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Originally Posted by zombie

Make sure the kessil cable isn't parallel to the probe wire. More than likely it's induced current/voltage on the probe wire.

You might be an engineer if...You have no life and can prove it mathematically.

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I reran the wire for the probe so it's not where near any other potential problem line. It's more consistent now but it's still doing the same thing. The only thing I can think of is that it shares the same section of the sump as the heaters? Maybe I'll try moving those.

I have the same issue. Had the same issue with the classic and now with 2016. One day salinity is running fine and next it just shoots up for no reason. Probe month old. I clean it every week with towel and rinse it around in tank. Normally runs way high for a few weeks then just drops back down then after a week or so goes back up. just back and forth. I even ran a PVC pipe through my wall and the probe cables run through it. NOTHING touches the cables yet just last night right at midnight it went from 34.60 to 35.40. ATO and floats etc all work correctly. My heater hasn't kicked on in forever (live in Lafayette La so always hot never need heater) so it cant be that. I cant figure it out for nothing but aggravates me. I've mentioned it to Neptune a few times and they keep saying its better to just watch for large swings than actual reading. thats a little annoying but they are doing the best they can with it, I get that, but sure wish someone could figure out the cause bc I cant... also I've verified it with a refractometer and a Milwaukee digital refract and both read 34 / 1.025. Also only other thing in that section of sump is the heater and skimmer. no cords come within 6 inches of power cables at any point. figured I'd join in bc if anyone figures it out i'd sure like to know.... Its the only thing I can say doesn't work properly on my apex. all else is perfect! (knock on wood)


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So I moved all of the probes to their own part of the sump. I separated the Salinity Probe as well. I was getting more consistent readings until (you guessed it) the lights went out and it immediately spiked up. I give up unless someone else has something to offer.

I am having the exact same issue right now. Mine has been calibrated and keeps doing the same thing

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If I check mine with the refractor it shows fine at 34 to 35% on the Apex it is jumping up to 37%

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Originally Posted by joenla

I have the same issue. Had the same issue with the classic and now with 2016. One day salinity is running fine and next it just shoots up for no reason. Probe month old. I clean it every week with towel and rinse it around in tank. Normally runs way high for a few weeks then just drops back down then after a week or so goes back up. just back and forth. I even ran a PVC pipe through my wall and the probe cables run through it. NOTHING touches the cables yet just last night right at midnight it went from 34.60 to 35.40. ATO and floats etc all work correctly. My heater hasn't kicked on in forever (live in Lafayette La so always hot never need heater) so it cant be that. I cant figure it out for nothing but aggravates me. I've mentioned it to Neptune a few times and they keep saying its better to just watch for large swings than actual reading. thats a little annoying but they are doing the best they can with it, I get that, but sure wish someone could figure out the cause bc I cant... also I've verified it with a refractometer and a Milwaukee digital refract and both read 34 / 1.025. Also only other thing in that section of sump is the heater and skimmer. no cords come within 6 inches of power cables at any point. figured I'd join in bc if anyone figures it out i'd sure like to know.... Its the only thing I can say doesn't work properly on my apex. all else is perfect! (knock on wood)


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34.5 ppt is 1.0261 sg
35.1 ppt is 1.0267 sg

The swing is within 0.001 sg. Your refractometer cannot measure that difference.


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On my new system, the conductivity goes up very consistently every night:

Attachment 8460


With the help of the Apex graphical logging, it didn't take long to figure out the reason. I have two heaters that take turns as primary and backup. In the early hours of the morning, when the tank lights are very dim and the house is rather cool, both heaters operate together much more often than during the day. The conductivity probe runs near the heater cords for only a short distance, but obviously enough.

Here's the above graph again , only now with superimposed red and blue traces for the two heaters. 'Purple' blocks, i.e. both heaters running, correspond to increased salinity readings. (Also, on the fourth trace, note the different kind of energy use peaks created by heaters at night, vs ramp up and ramp down of lights during the day.) I find these input graph comparisons to be a very useful Apex feature.

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