Crazy Conductivity Probe Issues

[adamk22]

The probe has worked perfectly since I got it about 7 months ago (see attached graph - very steady). Suddenly it spiked to from 34ppm to 40ppm with no changes to the 28 gallon nano. I didn't knock any salt creep back into the tank. I checked the tank water with a refractometer and it was spot on at 34.0 (also calibrated refractometer and retested, same result).
So I cleaned the probe, socked in vinegar, rinsed in RO and let dry. Then recalibrated the probe using 53,000 solution. Once the calibration completed, the calibration solution gave a reading of 35.0, but as soon as I placed the probe back in the tank it is now consistently reading 29.8ppm - What???
So, I dried the probe again and recalibrated using another fresh packet of calibration solution - same exact result.
Tried calibrating from Apex unit and through web interface - same result.
It's clear of electroical wires and interference.
I do have a second Temp probe attached and tried with and without 2.1 Conductivity Compensation.
Tank has chiller and never goes above 78.1 or below 77.9. I'm still not entirely clear on the compensation factor, but it used to work just fine with 0.0 compensation.
Everything had the latest firmware but I force a firmware update anyway on the whole APEX and on the PM2 - no dice.
I also restored all of the APEX settings from a backup taken a few days ago.
Strangest part, if I put the probe back in the calibration fluid it jumps from 29.8ppm up to 34.9ppm.
Any ideas are appreciated. I'm stumped. If I need a new probe I'm OK with that, but they aren't cheap and I only want to replace the probe if it will in fact fix the problem.
The agony and pain are worth it, I still love this stuff.

 

[cmacld]

I have had lots of issues with my probe since i got it... It has never calibrated correctly.
I will also get crazy jumps now and again, i usually find that some air or gunk has got in the probe, i give it a swirl and a light tap and it usually settles back to normal.

I have found that the best way for me to calibrate is to calibrate to the tank water, which works for me as i run at 35ppt. guess that would be tough if you didn't.

i read this a while back when i was searching for some of the same answers you were. Dont know if i can find the link again but i saved the instructions that were given by neptune to help solve this prob. I never tried it, but have been thinking about it as of late.

On a side note... i would never use my probe for exact measures, but i do like the piece of mind that i gives me in case of a leak or ato stuck on etc....

here ya go, hope this helps

neptune conductivity prob calibration.

1) Make sure the probe is completely dry (leave out of water for several hours after drying)
2) Prepare water bath at 77F and soak 53,000ms solution to bring up to temp
3) Place PM2 temp probe into water bath and wait till temp stabalizes (adjust temp calibration as required)
4) Start the calibration with dry probe stabalization first. Allow 30 - 60 seconds to stabalize
5) Place probe (hole facing up) in calibration solution and gently shake out any air bubbles. Angle the bag so more solution covers probe end.
6) When finished the reading should be 35ppt or 53,000ms
7) Adjust temp compensation as needed to achieve 35ppt or 53,000ms reading
8) Place probe in tank

 

[adamk22]

Thanks very much for the input. I dried the probe with compressed air. I'm out of calibration fluid, but my refractometer which is calibrated has my tank water at exactly 35, so I used the tank water to calibrate and now it seems to be back on track. I'll have to keep an eye on it.
An idea how long these probes are supposed to last before they should be replaced?

 

[cmacld]

not sure, i have had mine for a couple years now.. think i bought it when they first came out.

 

[schwaggs]

Could be electrical interference or stray voltage in your water. My Conductivity probe was rock solid for 2 years. The reading would vary no more the .3 all day long.

Then all of a sudden, 3 months ago I noticed the reading varying 1.4 units throughout the day. I tried adjusting the temperature compensation, tried cleaning and calibrating. I finally recognized that when my Frag tank halides come on, the Salinity reading drops 0.5 units. When the halides turn off, the Salinity reading jumps back up...

Try turning items off, waiting a few minutes, one at a time to see if it impacts your readings.