P4 Probe/sensor vs Refractor - Differing values

Lylelovett · Nov 30, 2018

Hi all,

I just got all my probes set up. All seem to be working great, but I have a question about my conductivity/salinity probe...

My probe is reading: 1.0238
My refractor is reading: 1.025

Is that an acceptable variance or should they be the same? I'm not sure what steps to take from here to rectify?

Thanks for your expertise.

Dree · Nov 30, 2018

I’ve never worked with probes in my aquarium, but plenty with my education I’m currently in. In my personal (and professional) opinion, I would consider the variance in your two reading unacceptable, or too much. BUT that is for my own liking.
Was the calibration process of the probe followed correctly? Also, is the probe placed near a heater? Is the outlet of the ATO before or after the probe? These are just a few questions to consider. Also, probes generally need a “break in” period, I noticed you wrote you just set them all up, so maybe wait ~2 weeks and compare the measurements again.

Vinny@GHLUSA · Nov 30, 2018

Don't expect these to match.

The conductivity probe is displaying values in kg/l.
Your refractometer shows values in S.G.

kg/l and S.G are different units of measurement, not 1:1 and are therefore not equal to each other.

EXAMPLE
If your refractometer shows 1.025 S.G., the kg/l equivalent is 1.022 at 77° F.

Given the difference of your actual readings, make sure BOTH the probe and refractometer have been correctly calibrated.

Here's a good tool to use for converting kg/l to the S.G unit of measurement:
https://www.hamzasreef.com/Contents/Calculators/WaterDensity.php

If you want to have the conductivity probe and refractometer display the same value, set the conductivity probe to display in PSU and look to the right of the chart in your refractometer. To the right, you will find the PPT measurment.

PSU = PPT

kodo28 · Nov 30, 2018

I use the PSU unit on Cond probe and when calibrating the probe I try to have the GHL solution at exactly 25°. You can used a temp gun to check it quick and easily

Calibrated the probe following the procedure on Profilux by making sure to set the temp probe as temp compensation if all good with the numbers you should get 50.00ms or 49.9ms once calibration is saved and still with the probe on solution.
Then you can check your water salinity which should be arround 53.1ms or 35PSU if you use the PSU unit.

Clark song · Dec 1, 2018

So, I want to know GHL’s recommendation how much it is at GHL probe. Thanks,

Clark song · Dec 1, 2018

So, I want to know GHL’s recommendation how much it is at GHL probe. Thanks,

Support@GHLUSA · Dec 1, 2018

Clark song said:
So, I want to know GHL’s recommendation how much it is at GHL probe. Thanks,

I'm sorry, I'm not understanding the question. How much what is?

Clark song · Dec 3, 2018

Marco@GHLUSA said:
I'm sorry, I'm not understanding the question. How much what is?

How much is it? for the recommendation value? It is 1.022kg/l for 25 c

Be102 · Dec 3, 2018

Marco@GHLUSA said:
I'm sorry, I'm not understanding the question. How much what is?

Can you maybe help me out Marco? My profilux is displaying 1.0061 at 79.1F . What am I looking at salinity levels in PPT. I tried to use the calculator you linked but got even more confused

Support@GHLUSA · Dec 4, 2018

Be102 said:
Can you maybe help me out Marco? My profilux is displaying 1.0061 at 79.1F . What am I looking at salinity levels in PPT. I tried to use the calculator you linked but got even more confused

If you're showing 1.0061 kg/l; then either you're running a very brackish water tank, or you have a number of other troubles. I'd inspect the probe; if there is growth on the tip, it will not read correct. If there is air bubbles at the tip, it will not read right. etc.. The Conductivity probes are very sensitive, need be kept clean without damaging the tip, and be kept free of bubbles which will skew the readings. Also need be calibrated properly.
Side note; 1.006 kg/l = ~12.5ppt / ~1.009 SG

Be102 · Dec 4, 2018

Marco@GHLUSA said:
If you're showing 1.0061 kg/l; then either you're running a very brackish water tank, or you have a number of other troubles. I'd inspect the probe; if there is growth on the tip, it will not read correct. If there is air bubbles at the tip, it will not read right. etc.. The Conductivity probes are very sensitive, need be kept clean without damaging the tip, and be kept free of bubbles which will skew the readings. Also need be calibrated properly.
Side note; 1.006 kg/l = ~12.5ppt / ~1.009 SG

Thanks Marco.. I switched it over to PSU to try to understand better and i believe my probe is just out of whack. If I was to go about recalibrating do i need to get more fluids from you guys? The current display is 11.9. @ 78'f.. I am unsure because my refractometer showed I was doing relatively close to the correct levels.

Can I put the probe in ro/di and find what the level its reading and then maybe go from there to fix it?

Thanks!

Support@GHLUSA · Dec 4, 2018

No, you don't want to use RODI to calibrate or "zero" reference the probe. As with any probe or sensor, you will want to calibrate or reference close to the actual measurements values.
You can purchase reference or calibration solution which would be appropriate.

Be102 · Dec 4, 2018

Marco@GHLUSA said:
No, you don't want to use RODI to calibrate or "zero" reference the probe. As with any probe or sensor, you will want to calibrate or reference close to the actual measurements values.
You can purchase reference or calibration solution which would be appropriate.

Hi Marco,
I just found that I have 3 fluids, maybe another somewhere...
ph 9.0
50 ms
220 mv

Will this be fine to set up probe correctly again? Am I missing a fourth? Looking @ the pics it shows 4 but I assume the temp one isn’t really a liquid. Maybe I am wrong.. it’s been awhile since I Set it all up