Salinity probe measures different values in and outside the tank

[SoNap]

Hi everyone,

since I have been using GHL, I have always had the problem that my salinity probe measured different values inside and outside the tank.

I'm currently sticking to the conductivity (according to the forum it seems that density would be more accurate but let's put this aside for the moment).
I recalibrated my probe one more time accuratelly and did the following test:

- probe inside tank -> 58,2mS
- probe in a plastic glas with some water from the aquarium -> 54,4mS

So there is a difference of approximately 4mS.

I expect the measurement outside the tank to be more or less correct.
Double checked this with Hanna Salinity tester (newly calibrated and verified against Fauna Marin and ATI reference solution).

I thought that this might be maybe related to some leakage current in the tank so I installed the Deltec Titanium grounding probe (and I'm also using a Titanium heater) but this didn't really solve the issue (also checked the grounding on the socket and it looks correct).
I'm running out of ideas what would cause the probe to measure inside the tank a higher conductivity compared to outside the tank?

I really appreciate if you have maybe any other hint or can shed some light on this.

 

[Dave-T]

When the probe is in your tank, is it fully submerged? I had a problem where my probe stopped working when it was fully submerged.

 

[SoNap]

No, it is not fully submerged. Only the lower part, i.e. the first 4-5 cm, is in the water.

I also tried to put the probe in different locations in my sump but this also does not change anything.

 

[Pod_01]

Hi everyone,

since I have been using GHL, I have always had the problem that my salinity probe measured different values inside and outside the tank.

I'm currently sticking to the conductivity (according to the forum it seems that density would be more accurate but let's put this aside for the moment).
I recalibrated my probe one more time accuratelly and did the following test:

- probe inside tank -> 58,2mS
- probe in a plastic glas with some water from the aquarium -> 54,4mS

So there is a difference of approximately 4mS.

I expect the measurement outside the tank to be more or less correct.
Double checked this with Hanna Salinity tester (newly calibrated and verified against Fauna Marin and ATI reference solution).

I thought that this might be maybe related to some leakage current in the tank so I installed the Deltec Titanium grounding probe (and I'm also using a Titanium heater) but this didn't really solve the issue (also checked the grounding on the socket and it looks correct).
I'm running out of ideas what would cause the probe to measure inside the tank a higher conductivity compared to outside the tank?

I really appreciate if you have maybe any other hint or can shed some light on this.

Just a suggestion but put the salinity probe and temperature probe in the cup. Maybe the temperature change is impacting your measurement.

 

[Vinny@GHLUSA]

You can always re-calibrate, then let it sit in the 50mS solution for 5-10 minutes. Come back to it and see what it shows for a value. Also check the probe tip for any damage to the two prongs. Neither should be bent.

 

[SoNap]

@Pod_01:
unfortunatelly this does also not change the fact that the salinity in the cup is somehow lower (kept both probes, temp and salinity, for around 30 minutes in the cup)

@Vinny@GHLUSA:
thanks for your input but do you really think this might explain the difference of the measured value?
No matter if for example somehow the calibration was not done accurate enough or if the prongs are bent, I would in both cases not really expect that the value is different. Or am I wrong on this?

But anyway, will get today a new 50mS solution in order to make sure that the current one that I'm using is maybe not contaminated somehow (by the way I also tried to calibrate the probe using other non GHL reference solution with 35 PSU by using 53,1mS but this also does not resolve the issue that I have).

 

[Vinny@GHLUSA]

@Vinny@GHLUSA:
thanks for your input but do you really think this might explain the difference of the measured value?
No matter if for example somehow the calibration was not done accurate enough or if the prongs are bent, I would in both cases not really expect that the value is different. Or am I wrong on this?

But anyway, will get today a new 50mS solution in order to make sure that the current one that I'm using is maybe not contaminated somehow (by the way I also tried to calibrate the probe using other non GHL reference solution with 35 PSU by using 53,1mS but this also does not resolve the issue that I have).

Before looking for a reason for the difference, one should first verify the probe is providing the correct values in the first place. Once this is confirmed with a fresh bottle of 50mS reference fluid, you can troubleshoot the cause of the original concern.

 

[Pod_01]

@Pod_01:
unfortunatelly this does also not change the fact that the salinity in the cup is somehow lower (kept both probes, temp and salinity, for around 30 minutes in the cup

Interesting, let us know how this develops.
I find that the GHL salinity probe has its own personality.

So I don’t use it for anything absolute. Instead I just use it as relative measure. Is salinity going up over time or down.

Good luck,

 

[Vinny@GHLUSA]

Interesting, let us know how this develops.
I find that the GHL salinity probe has its own personality.

So I don’t use it for anything absolute. Instead I just use it as relative measure. Is salinity going up over time or down.

Good luck,

According to your chart, the min and max reported values are:
34.2 PSU - 34.9 PSU

Although your chart looks exaggerated, it's really not bad at all.

In S.G, that converts to 1.0258 - 1.0263...which means you're getting a daily swing of only 0.0005 SG.
Are you really looking for something even more "absolute"?

For an even tighter swing, you'd have to stabilize your temperature some more. Any swings there will affect the conductivity of water.

 

[Pod_01]

According to your chart, the min and max reported values are:
34.2 PSU - 34.9 PSU

Although your chart looks exaggerated, it's really not bad at all.

In S.G, that converts to 1.0258 - 1.0263...which means you're getting a daily swing of only 0.0005 SG.
Are you really looking for something even more "absolute"?

For an even tighter swing, you'd have to stabilize your temperature some more. Any swings there will affect the conductivity of water.

When I got it I was expecting flatter line lol. Expectations vs. reality and lack of experience.
I honestly didn’t think there would be much of a variation and as a new user with high end toy I was, do I add salt no RO water etc… .
But, I got that out of my system and I am good now.
Sometimes it does drop to 33 or 32 but I suspect some contaminants and then it is back to normal reading or I clean it.

Overall I am good with the probe, it has been in use for 5 years and it keeps on working.

Interesting on the temperature comment, I knew the salinity probe uses temperature but I didn’t think that temperature swing would impact the reading. Thanks.

 

[Vinny@GHLUSA]

When I got it I was expecting flatter line lol. Expectations vs. reality and lack of experience.
I honestly didn’t think there would be much of a variation and as a new user with high end toy I was, do I add salt no RO water etc… .
But, I got that out of my system and I am good now.
Sometimes it does drop to 33 or 32 but I suspect some contaminants and then it is back to normal reading or I clean it.

Overall I am good with the probe, it has been in use for 5 years and it keeps on working.

Interesting on the temperature comment, I knew the salinity probe uses temperature but I didn’t think that temperature swing would impact the reading. Thanks.

Wow!
5 years for a single probe is amazing! Quite the possibly a new record. Most usually replace at the 2 year mark.

 

[Pod_01]

Wow!
5 years for a single probe is amazing! Quite the possibly a new record. Most usually replace at the 2 year mark.

Just double checked and I ordered the ProfiLux4 set on Septembers 19/ 2018 and so far I am using all of the 4 original sensors.

Few months back I was bit worried about the pH sensor so I stuck it into brand new calibration fluid and it was off by 0.01 pH.
What does surprise me a bit is that my last calibration was done 3+ years ago, yet they do seem to measure just fine.

Fingers crossed, hope they last another 5 years…