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Problems with Salinity Probe

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speyside712 View Drop Down
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    Posted: October 23 2017 at 2:41pm
Hey guys,
I'm having some difficultly getting a salinity probe to work with my Apex Classic and the PM2 module.  I've read about a million online forums and have a pretty good idea what the problem is, but it seems difficult to solve.

Basically, regardless of how many times I calibrate this thing, I can never get an accurate reading inside the tank for more than a few hours.  I believe microbubbles and electrical interference is the problem, but both of these issues seem nearly impossible to avoid.  My readings seem random at times, and when I do get it to read something that sounds reasonable like 34 ppm then it slowly creeps up 1ppm per hour every hour until i recalibrate it and try again after its up to 50 ppm.

I can't find a single square inch of my tank that does not collect microbubbles, especially not in the sump.  My sump is laid out with 3 compartments, first is the filter socks and skimmer, second is the refugium, third is the return pump, reactor pump, with the ATO and Dosing pumps depositing here.

I don't see any bubbles and the water looks pretty clear, but if I leave anything in any of the 3 compartments for more than an hour or so i find a layer of bubbles attached to the bottom.  I'm starting to think the display tank might be my best bet, as awful as that sounds.  Currently I have the probe in the return pump section, as this area seems to have the least bubbles.  This isn't ideal because the ATO and dosing pumps output here, which will mess with the reading temporarily while they are running, but i'm just trying anything to get it to work right now.

I have a bubble trap in the sump right before the return pump, and I have filter pads in the bubble trap, but i still seem to have enough microscopic bubbles get through to mess with the reading.  Currently its showing 48 ppm, which is clearly wrong.  As my refractometer and hydrometer are both reading 1.025 (and the fact that everything would be dead already if it was that high).

I have been extra careful when calibrating it to get all the bubbles out, I used a probe storage bottle, filled the bottle with the 53,000 solution and put the probe in.  This way I can turn the probe completely upside down while calibrating in order to get all the bubbles out.  When putting the probe in the tank i do the same and put it completely upside down for a moment, shake all the bubbles out, then install it in the probe holder without ever lifting the tip above the water line.  I have my probe holder set to hold the probes bottom inch and half in the water, with the rest exposed to the air.  Even with this deliberate method, my reading is still often way to low or way to high.  I've tried calibrating a few times now.


The other problem i'm having is probably from the electrical interference from other equipment.

How on earth are we supposed to "isolate the probe and its cord from all other electrical equipment."  That seems completely impossible.  A reef tank has something like 2000 watts running to it 24/7, with probably 25 outlets plugged in, most of which are running to the sump, right next to the probe.  Not to mention the PM2 is mounted on a mounting board where every single one of those 25 outlets all converge.  How could we possibly isolate the probe and its wiring from all of that?  Can't neptune fix this by just insulating the probe and its wire with a thicker coating?

It seems to me like for the price of this thing it should come pre-calibrated where you can just put it in the water and have it work....

I know many people on this forum use the apex and this same probe.  What have you done to make it work for you?  Do you have an extra compartment in your sump that I don't have, shielded from all possible sources of bubbles?  Does your bubble trap work better than mine?  Do you have a 2nd fish room with nothing in it but your PM2 and salinity probe wire to keep it isolated? lol, ok maybe that last one was a joke...

I've about had it with this apex, as i'm having similar problems with the ph and temp probes as well...but I won't go into those issues in this post.  I'll save that for my next one haha
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Krazie4Acans View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: October 23 2017 at 3:00pm
I have a few questions before I offer up any solutions. First one is is there evidence of electrical leakage in your tank and do you run a grounding probe?

Do your probe cables run parallel and along the same route as your power cables?

Your salinity probe has a small hole in the side of it. Have you tried mounting it at a 45 degree angle with that hole pointing to the top and out of the water?

Is this a lab grade probe and standard grade probe, a Neptune probe or some other brand?

You mention inverting the calibration solution during the calibration. Do you also float that solution in your sump prior to calibration as well as during the calibration to keep it the same temp as your tank?

What does the probe do if you place it in a cup of tank water that is sitting in your stand but not in the sump?


Edited by Krazie4Acans - October 23 2017 at 3:02pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: October 23 2017 at 10:40pm
I agree with Jeff's questions. The answers will help you find the solution. I believe the other probe's problems are related to this probes problem, so it would be good to describe the other probe issues.

Electricity is funny, yet fascinating. There is a thing, I think it may be called induction transference or something like that. Wires running parallel without sufficient shielding can pick up each others signals. Plastic insulation, no matter how thick (within reason), does nothing to prevent this interference. An electromagnetic (EM) field that surrounds and/or encompasses an electrical wire, especially a wire from a sensor meant to communicate very tiny changes in voltage or current, can mess with sensitive electronic circuits, causing inaccurate readings.

It's not all bad. Broadly speaking, EM Induction is what powers our impeller driven aquarium pumps, charges our electronic toothbrushes, and many other useful things. In fact it's how electricity is generated. Smile

Good luck
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Post Options Post Options   Thanks (0) Thanks(0)   Quote speyside712 Quote  Post ReplyReply Direct Link To This Post Posted: October 23 2017 at 11:04pm
I have the Neptune Systems Lab Grade Conductivity/Salinity probe.

I am not using a grounding probe.

I floated the solution in my sump for about 20 minutes so that it would be the same temperature as my tank water. I am using 2 temperature probes, 1 connected to the apex head unit and one connected to the PM2. I have the temperature adjustment set to 2.2 on the conductivity probe and I have calibrated the temperature probes to be accurate.

The probe has been in the sump all day today reading around 47 ppm. I watched the ATO come on for a moment and the number went down about .5 ppm, then slowly trickled up over the next few hours toward 48 before the ATO ticked on again. Clearly those numbers are off, but I can see that it is going down when it should and up when it should, so at least the trend is right.

I put the probe in a cup of tank water outside the sump, shook the bubbles out, and it jumped all the way to 60 ppm. Then I put it back in the sump, shook the bubbles out again and now it shows 69 ppm. Each time I gave it a few minutes for the number on the fusion display to settle.

As for the wiring, all of my wiring goes through one 2.5 inch hole in the drywall behind the sump, into my "fish closet." I have a second hole in the drywall used for the small plumbing (dosing pumps and ATO). It is about a foot below the wiring hole. I tried moving the probe cable into the hole with the plumbing instead so it is no longer with all the other electrical wiring, but this didnt change the measurement. All of my wiring comes together at the mounting board, so I tried to run the probe cable as far from those as possible until it gets close to them where it attaches to the PM2. I still didn't get any change in the measurement though.


I am assuming the bubbles inside would make the probe read too low, so if it were calibrated with bubbles inside then the normal reading would be way too high once said bubbles were removed(as mine is).

I am out of calibration solution, but as soon as some more arrives in the mail I will try again.


So, assuming I can get it calibrated correctly, how do you prevent bubbles from getting to it in the sump if it is so easily thrown off by a couple tiny microbubbles? Is the probe water tight enough to mount it upside down fully submerged? That would solve the bubble problem.

Edited by speyside712 - October 24 2017 at 7:15am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: October 24 2017 at 10:19am
What about the other probes? What is the story with them?

I believe it would be helpful to check for stray voltage with a voltage meter. Anything over ~25 volts could be messing with your Neptune. A grounding probe may even be a Neptune recommendation, I don't know. Voltage over ~60 volts is serious. It usually means there is cracked insulation on a wire in or near the water. Sometimes it's a faulty heater. The Neptune probes could actually be acting as a grounding probe. Shocked Might need to unplug the Neptune to do this check.

Could it be a bad connection somewhere? One of my LED fixtures had intermittent problems ever since I had acquired it. It recently went out during the day. It had been ON in the morning. Confused I had previously fixed a problem where I had to re-solder the wires in the DC power plug because they frayed and started touching/short circuiting. It's an old programmable/dimmable black box fixture. I opened the box and started checking the wires from the power plug to the circuit board. Sure enough, one of the easy disconnect clips had been going bad. There was carbon all over one of the prongs, caused by electricity arcing. This had probably been going on for a long time. Ouch I'm glad I was able to find and fix it so easily. Big smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: October 24 2017 at 10:42am
While the recommendation of less than 25 volts is good for most things, the conductivity probe measures micro volts to determine the salinity. Thus any voltage that has a path to ground (read that as allows current to flow through the water) can effect the reading.

I'm assuming that you only set the temperature compensation to 2.2 after you have calibrated the probe and that you remove that before calibrating it again, right? What is the temp of your tank water when you are doing the calibration? 77 is the sweet spot.

Check the hole in the side of the probe tube for blockage. It should allow air to escape through it so that micro bubble don't build up in the probe.

The probe is not sealed well enough to mount it upside down in the water. Neptune actually warns about this in the CUG.

Routing cables through the same hole in the wall is not really an issue unless they are then all bundled together the rest of the way to the controller. you want probe and other non-power cables to run perpendicular to the power cables and only parallel when absolutely needed.

I really suspect you have stray voltage in the tank that is effecting all of your probes. you could test this by turning off all pumps, heaters. powerheads, lights and for a few minutes and see if the measurements normalize. The cup test should have sown this as well. but the results there are inconclusive.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark Peterson Quote  Post ReplyReply Direct Link To This Post Posted: October 24 2017 at 2:54pm
Originally posted by Krazie4Acans Krazie4Acans wrote:

While the recommendation of less than 25 volts is good for most things, the conductivity probe measures micro volts to determine the salinity. Thus any voltage that has a path to ground (read that as allows current to flow through the water) can effect the reading.
Good point. That makes sense, as does the use of the Neptune itself to check for stray voltage. Typically we hook up the Voltage Meter and unplug equipment one at a time to find which one is the culprit, but I like Jeff's Lamp of using the Neptune to find the culprit. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote speyside712 Quote  Post ReplyReply Direct Link To This Post Posted: October 26 2017 at 4:56pm
Hey guys, I did a little bit more troubleshooting to try and find answers to these questions you have.

Mark - The story with the other probes is 1 of my ph probes is clearly broken, and i believe unrelated to the salinity issue.  I bought 2 used from a fellow reefer here on UtahReefs.  One of them works fine, but the other is way off and refuses to calibrate.  It seems to think the 7.0 ph solution has a higher ph than the 10.0 solution.  I swapped the port each probe was using on the apex head unit and the bad one had the same problem in the other port, while the good one calibrated just fine in either location.

I have since ordered a new replacement ph probe to fix this.  I think we can write this off as being unrelated, since the probe itself was the problem here.

The two temperature probes I bought read 3 degrees apart even when they were 2 inches from eachother.  I calibrated them both using 3 regular old school thermometers and averaging the results of the 3.  Now they are exactly the same when near eachother and are working well.



Back to the salinity probe issue - One at a time I turned off every item in the water (by using the apex to kill power to each outlet).  I watched the conductivity measurement for a few minutes after turning each one off, giving it time to update in Fusion.  Even after turning off every item I did not experience any change to the conductivity measurement.  That leads me to believe that stray electricity is not the problem.  I ordered a grounding probe anyway just to be safe, as they are only 15 bucks or so, but I don't think that will fix the problem.


My new calibration solution packets arrived today, so i'm going to give re-calibrating it a shot.
I raised the level of water in my sump about 2 inches, this significantly cut down on the bubbles entering the return pump section.  I am hoping with a simple re-calibration that my problems will be solved.


Jeff, you mentioned I should only change the temperature compensation AFTER calibrating the probe.  That was not what a BRS Youtube video stated, in their "how to calibrate a conductivity probe" video.  But maybe that is my problem.  I changed the compensation to 2.2 BEFORE calibrating.

Personally i don't really understand the purpose of the temperature compensation.  If i am calibrating my probe at the same temperature it is always going to be used at then what value is the compensation feature adding?  I only set it to 2.2 because the BRS video i watched suggested that.



Edited by speyside712 - October 26 2017 at 4:57pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Krazie4Acans Quote  Post ReplyReply Direct Link To This Post Posted: October 26 2017 at 5:29pm
You mention that you turned off each item individually and didn't see a change but did you turn them all off at the same time? I ask because it could actually be more than one device leaking voltage. Turning them all off for a short time would show this effect and then turning each item on one at a time would show one of the devices add it was turned on. Then you could turn that one back off and continue until you find any other devices that might be leaking.

As far as the temperature compensation goes. This is highly dependant on your tank temperature at the time of calibration. As I mentioned before the calibration solution is only truly accurate at 77 degrees. That is the temp that the manufacturers produce their solutions to be accurate. Temperature changes  from that will effect the reading. So calibrating the probe at 77 degrees and then setting the compensation value to 2.2 will account for the charges in temp away from 77. Keep in mind that if you are only tracking values outside the normal readings this level of accuracy is a little extreme. [😊]

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Post Options Post Options   Thanks (0) Thanks(0)   Quote speyside712 Quote  Post ReplyReply Direct Link To This Post Posted: October 28 2017 at 7:06pm
What I should have said was that I turned each item off one at a time until everything was off at the same time. Just like you are suggesting.

Well anyway though, good news! I think I have it working now. I floated the bag in my 77.7 degree tank water for 15 minutes or so, then I cut open the bag and poured some into a probe storage vial. I calibrated the probe dry (it had been sitting dry for 48 hours to ensure no droplets were still in the tube). Then I calibrated the probe in the 53000 solution upside down in the probe storage vial, to ensure all the bubbles were out. All of this was done with the temperature compensation set to 0. Bingo, it seems to have worked this time.

After placing it in my tank and swishing it around upside down to remove all the bubbles it was showing 31.3 PPM. I set the temperature. Compensation to 2.2 and the probe dropped to read 30.9 PPM and stayed there for over an hour now. That is right on with what my refractometer is reading. So assuming it holds here overnight then I think I can close the case!

Thanks for the help Jeff and Mark, you guys always know what your talking about yet have completely different approaches to how to fix things. It helps to get a few different viewpoints and ideas about these things.

Edited by speyside712 - October 28 2017 at 7:08pm
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