Refractometer or conductivity probe?

[CraigH]

I've calibrated my conductivity probe on my new P4 in the 50ms fluid with the fluid floating in the sump (in a bag) next to the temp sensor and it's currently reading 1.0241 whereas my refractometer reads 1.026 - 1.027 (temp compensating D-D). The refractometer is calibrated using 35ppt fluid.

Which do I trust? Can I adjust the reading of the probe to match the refractometer?

Thanks

[Thilo]

Please check the refractometer and the conductivity sensor with the 50ms fluid. Then you can see which one shows a wrong value and recalibrate.
If you want to adjust the reading you can do that in GHL Control Center on the sensor page input field "Density-Offset".

[CraigH]

What will the 50ms fluid calibrate to on a refractometer?

[Thilo]

50ms = 32.738ppt = 1.0247sg = 1.0247kg/l

Conversion done here: https://www.hamzasreef.com/Contents/Calculators/SalinityConversion.php

[alekslyse]

I prefer this calculator https://reefapp.net/en/maintenance/calculator/unitconversion - it will make sure to give you the convertion with temperature adjustment.

[alekslyse]

50ms = 32.738ppt = 1.0247sg = 1.0247kg/l

Conversion done here: https://www.hamzasreef.com/Contents/Calculators/SalinityConversion.php

I have been wondering a bit how the P4 calculate the salinity numbers:

My temp @ 25.5c P4 measures: 51.9ms - 33.9PSU - 1.024KG/l
Calculator @25.5c: 59.9ms - 33.9PSU- 1.0223 g/cm³ -1.0254 sg
Calculator @ 25c: 59.9ms - 1.0224 g/cm³ - 1.0254 sg

For me it seems like the P4 is calcuating @ 25c regardless of tank remperature. Would it be possible to force the calculation to be made by real temperature and get sg as well as KG/L?

[CraigH]

50ms = 32.738ppt = 1.0247sg = 1.0247kg/l

Conversion done here: https://www.hamzasreef.com/Contents/Calculators/SalinityConversion.php

Well the 50ms GHL fluid is 25ppt on my refractometer, what is the calibration fluid made of? Does it have a proper refractive index like seawater?

Surely the D-D refractometer isn't that far out?

[alekslyse]

Well the 50ms GHL fluid is 25ppt on my refractometer, what is the calibration fluid made of? Does it have a proper refractive index like seawater?

Surely the D-D refractometer isn't that far out?

Did you try to calibrate your refractometer with osmos water? It should be at 0 with it

[CraigH]

Did you try to calibrate your refractometer with osmos water? It should be at 0 with it

Yes, 0 TDS RODI water tests as 0 on the refractometer

[alekslyse]

Yes, 0 TDS RODI water tests as 0 on the refractometer

What is the ms recorded (not kg/l)? What is your tank temperature at the same time as your report your ms?

[CraigH]

What is the ms recorded (not kg/l)? What is your tank temperature at the same time as your report your ms?

My refractometer won't give an ms reading only ppt or sg. The tank is currently at 26c and 51.9ms according to P4. Refractometer gives 1.026 (34ppt) @ ~20c

[alekslyse]

My refractometer won't give an ms reading only ppt or sg. The tank is currently at 26c and 51.9ms according to P4. Refractometer gives 1.026 (34ppt) @ ~20c

Check your temperature probe. @ 26 degrees 51.9 = 1.0251 @ 25 degrees = 1.0257 - use a glass of rodi icecubes and water to find absolutely zero on your probe in case its off

[Mortie31]

I would buy salinity calibration fluid at 35ppt and calibrate your refractometer with that, IMO RO water or sterilised water or any such liquid doesn’t give accurate calibration as it’s set point (ie 0) is too far away from what your asking it to measure.

[tbreza]

I’ve found that when my refractometer and conductivity probe don’t match, it’s because of micro bubbles on the probe. I have my probe in front of a powerhead in my sump and that keeps it reading perfect.

[doggydoc10]

I’ve found that when my refractometer and conductivity probe don’t match, it’s because of micro bubbles on the probe. I have my probe in front of a powerhead in my sump and that keeps it reading perfect.



Same here.
A powerhead in front of probes works perfect.


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