Conductivity Probe values drifting down

I have set up the Profilux 4 to monitor conductivity with a goal of 53mS. I have it assigned temperature compensation as "Temperature 1". I have ATO with Tunze and Temp stable at 26 degrees. When I set up the probe the conductivity reads 53.2 and slowly drops over a day or two to where it is now 52mS. I have checked the aquarium (Reefer XL 450) for leaks and it is intact. I haver looked for salt creep and find none.
I therefore am concluding that there is an issue with the probe or software reading it. Can I get assistance with this?

Conductivity should be roughly proportional to salinity so you need to check this with a calibrated refractometer. That being said I think that it's mainly useful for trends - meaning that my tank will have a different conductivity than yours even with the same s.g.

My tank is stable at 60.5mS with SG of 1.026 with a calibrated refractometer. I noticed it creep up to 61.3 over a day or so and found that my ATO was set a bit low and SG had crept up to 1.028. Later after a 10% water change my conductivity changed to the 61 range at the same S.G.

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Originally Posted by clumeng

Conductivity should be roughly proportional to salinity so you need to check this with a calibrated refractometer. That being said I think that it's mainly useful for trends - meaning that my tank will have a different conductivity than yours even with the same s.g.

My tank is stable at 60.5mS with SG of 1.026 with a calibrated refractometer. I noticed it creep up to 61.3 over a day or so and found that my ATO was set a bit low and SG had crept up to 1.028. Later after a 10% water change my conductivity changed to the 61 range at the same S.G.

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I really appreciate that you are trying to help but I think that the temperature corrected calibration fluid should be the most scientific way to calibrate a brand new probe. The refractometer is not temperature corrected and may itself be in error. I believe that something is happening to the probe but I don't know what. When I lift it out of the water and shake it and place it back in, the level goes back up. I have it placed in an area of high current aw2ay from air bubbles. and my ATO keeps the s.g. extremely stable.

I really would;d like to hear from the company on this and may have to go directly to support. I thought that this was the appropriate way to get help from them but perhaps it is not.

I have the same issue.
My ATO is stable, my salt level also.
I messured over years with an IKS Aquastar and IKS platin probe without the effect of down drifting conductivity.
As I got the brand new PL4 set, I followed the calibration instructions and compared the result with the old IKS platin probe messures. It was nearly the same.
After a few days, sometimes hours - the conductivity level drops drifts down a lot.
Also I have place both probes in the same holder to test if there is an issue with the GHL probe.
The IKS probe stays stable and the GHL probe drifts down after 1-3 days. If i shake the GHL probe - both levels are the same.
There are no air bubbles, algae or something else near to the probes.
If needed, I can shoot some comparism pictures of both computers and their measurements.

Whats the cause for that? I also add an extra shielding (alluminium) for testing without any effects...

It's a bug in the system. It must be. I'm having the exact same issue. You can "reset" the downward drifting by pulling the conductivity probe out of the water for a second and putting it back in. When I do this, it resets the downward drifting effect.

I calibrated my brand new conductivity probe correctly (floating the 50 ms solution to equal the right temp) and when I initially put the probe in the tank, it reads correctly (matching with my freshly calibrated refractometer).
Over the course of about 12 hours, the salinity slowly drifts downward on the conductivity probe. I rechecked the measurement with the refractometer and everything was exactly the same.
I recalibrated the probe and put it back in, it now matched the refractometer again perfectly.
Over the course of 12 hours, the probe again drifted downward, from about 1.0265 to 1.0235 (a pretty big downward drift).
I pulled the probe out of the water for a second and put it back in. It now reads correctly, but I'm assuming it's going to drift downward again.

Definitely either a batch of defective sensors or defective software.

i also notice this thing.. same issues with my PL4

Hi

I can't find any errors in our test systems in regards to salinity. We also have meanwhile several hundred of new P4 owners, I doubt that there is a system error.
The values in our test systems are plausible and without significant drifting.

The hardware and firmware parts of the conductivity measurement (incl. temp. compensation) are practically the same as found in the P3, and the P3 is working fine for over 9 years now ...

The conductivity measurement is extremely depending on a correct temperature measurement for the compensation, maybe there is the reason.

The temp. during the calibration must be 100% correct (best way to do so: have the calibration fluid bottle floating in your tank for a few hours so it has the same temp. as the tank water).

Later the cond. probe must be very close to the temp. probe during operation.

Maybe calibrate again.

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You can "reset" the downward drifting by pulling the conductivity probe out of the water for a second and putting it back in. When I do this, it resets the downward drifting effect.

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I have no logical explanation for this. The probe just measures the resistance of the water between 2 electrodes, nothing else.
If you remove the probe out of the tank the probe temp. will change.

Or maybe moving the probe eliminated coincidentally the real problem, like air, algaes, snails, ...

i will do another calibration tonight with method of floating bottles.. but i have 23 C in tank.. must setup this temp on calibration request?? (standard set at 25 for reference solution)

you must enter the temp. your fluid has in the moment of the calibration

yes yesterday i do with my own digital thermometer .. but also today swirl down around 0.5 psu ..

there is a simple test to check if the measurement is correct:

1. do a precise calibration - fluid bottle for some hours in tank, use the tank water temp. as reference during calibration

2.leave the bottle in the tank: put the probe into the fluid (which has tank temp.) and check if it shows 50.0mS (+/-0.2 is OK and normal)

of course the tank temp. probe must be used for compensation

ok perfect..thank you matthias i'll let you know.

- conductivity probe is brand new
- Calibrated, and re-calibrated following manual (with floating 50ms fluid in tank water for several hours to ensure equal temp)
- no algae or bubbles on probe (it's brand new; plus it's in my sump on a probe holder right next to the temperature probe. The skimmer is in a chamber downstream of probe)
- consistently seeing a downward trend in my conductivity reading. I have the past 18 hours of data I can share, which shows "part" of the downward trend. I havn't figured out a way to compile all the previous data saved into one long graph.
- temperature is stable with +- .5 degree F

Attachment 9005

- Took probe and pulled it out of the water (for 2 seconds)
- placed probe back in sensor holder
- waited 5 minutes (in case any temperature difference from removing from water for 2 seconds)
- new reading of conductivity is 35.5 PSU, which is 1.6 PSU (parts per thousand) higher than before removing from water for 2 seconds.Attachment 9006
- Awaiting new graph data (going to record over 24 hour period, and show drifting effects)

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Originally Posted by dawsokj1988

- Took probe and pulled it out of the water (for 2 seconds)
- placed probe back in sensor holder
- waited 5 minutes (in case any temperature difference from removing from water for 2 seconds)
- new reading of conductivity is 35.5 PSU, which is 1.6 PSU (parts per thousand) higher than before removing from water for 2 seconds.Attachment 9006
- Awaiting new graph data (going to record over 24 hour period, and show drifting effects)

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This is all very interesting doesn't tell us much.
Please let us stay with the measured base unit (mS), all other values are calculated.
Put for a test the probe into the fluid bottle which has been floating all the day in your sump (where the probe is). This reading (must be 50mS +/-0.2) is interesting.
I assume the calibration fluid was floating in the sump before calibration since the probes are there, too.

Hi guys.. i recalibrated yesterday (after update GCC and P4 new firmware ) all process is done correctly with floatind bottles and controlled temperatures.

Yesterday 35.1 PSU

this morning 34.3 PSU

..

I just tested a theory, and it worked.

The issue I believe is microbubbles. This explains why pulling it out of the water for 2 seconds and putting it back in would correct the conductivity reading.

I tested it by allowing the probe to sit in the sump for 12 hours. Over this 12 hours the conductivity drifted from 54ms to 49.2ms. I then took a turkey baster and blew the probe with some water (without pulling it out of the water), and the readings corrected to 54ms.

I'm going to move the probe in front of the inflow and see if the high flow will eliminate the microbubbles (thus confirming the theory).

Well I moved the probe to in front of the inflow area (with high flow), and I'm still having the same issue. If it is microbubbles, how is this solved? I'm reading posts of people using different conductivity sensors 2 cm away from the pl4 sensor for reference. The pl4 sensor is giving erratic readings, while the other sensor is giving normal readings. Is it just the design of the probe that makes it highly susceptable to microbubbles?

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Originally Posted by dawsokj1988

Is it just the design of the probe that makes it highly susceptable to microbubbles?

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I do not know. Matthias has said in another thread, that a lot of people are using the PL3 and they still have no problems.
Also a few threads above someone is using a PL3 and a PL4 together and only the PL4 has issues.
I am new to GHL with the PL4 but if I understand the other posts correctly - the probe design has not changed and the PL3 seems to have no problems in reading a consistent cunductivity.
My Probe is drifting more than 5 percent and I need a solution for that.
Actually I can not trust the probe... I tried all possible locations in the sump. Next and final try is a housing for the sensor. If this is not working, I will borrow me a PL3 from a friend (who is also using the PL4 since yesterday- but for freshwater) and test my probe with the PL3....

I have been measuring conductivty on my new P4 for 3 weeks with exactly the same problem. I have tried recalibration as described before but up to now no success. Has anyone found a solution to this?

So I have continued to experience a problem with the probe. Even placing the probe in an area of high flow shows a slow steady decline in readings. I understand the micro bubble theory but it renders the probe as an unreliable and ultimately a mostly useless piece of equipment. If I want a reliable reading it requires me to remove the probe, shake it off, put it back in the water and wait for it to stabilize. This does not fit with the intended design of a continuous monitoring probe. I am not sure how to resolve this. I will most likely contact support directly or try posting on R2R.

kvarano,

This issue has been solved since May. We asked customers who has had these issues to please contact us for their replacement probe.

Please see post 46 for contact info:
http://forum.aquariumcomputer.com/sh...very-day/page5

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Originally Posted by Vinny

kvarano,

This issue has been solved since May. We asked customers who has had these issues to please contact us for their replacement probe.

Please see post 46 for contact info:
http://forum.aquariumcomputer.com/sh...very-day/page5

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Thank you Vinny. I lead a very busy life and this is the first I have followed up and did not see the other thread. I will contact GHL support.

I have the same issue for a year with my P3 set. When I take the probe out of water for a seconds and put it back, the value will be correct. After one or two days, the value will drifting down again.
I belive your theory is right,How to solve it? Thanks.

Hello,

Same problems with conductivity probe even with all the suggested solutions from other folks here, re-calibration, new place in relation with flow etc, etc. Was not possible to wait for new probes from GHL because of my installations.

-> Best solution so far for me: 3 conductivity probes bought from Atlas Scientific 1.0 K: extremely reliable and **stable** for a fraction or the cost. Extremely fast delivery (4 days).

I'm not frus strated anymore now! Good luck!!

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Originally Posted by pcadieux

Hello,

Same problems with conductivity probe even with all the suggested solutions from other folks here, re-calibration, new place in relation with flow etc, etc. Was not possible to wait for new probes from GHL because of my installations.

-> Best solution so far for me: 3 conductivity probes bought from Atlas Scientific 1.0 K: extremely reliable and **stable** for a fraction or the cost. Extremely fast delivery (4 days).

I'm not frus strated anymore now! Good luck!!

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Hi.
I’ve just installed my new Profilux 4. I had some issues calibrating the conductivity probe. Second time, I’ve kept the solution bottle floating. Still the reading was still far from a RedSea refractometer. I will try for a third time the calibration. Still, the Atlas Scientific probe....it works directly with the Profilux, or you had to do some improvisation? Thanks

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Originally Posted by cristimv

Hi.
I’ve just installed my new Profilux 4. I had some issues calibrating the conductivity probe. Second time, I’ve kept the solution bottle floating. Still the reading was still far from a RedSea refractometer. I will try for a third time the calibration. Still, the Atlas Scientific probe....it works directly with the Profilux, or you had to do some improvisation? Thanks

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Hello Cristimv,

Five weeks now of continuous use and they are reliable and stable.

Good luck!

Pierre