Conducrivity sensor problem

[progman]

I calibrated the conductivity sensor.
First time with 50 ms liquid
Second time with 53ms liquid ( it is 35 ppt of salinity )
The probe shows 33.8 ppt of salinity of water in my tank in both cases.

But optical refractometer shows 35 ppt in the my tank!
I calibrated optical refractometer with 35 ppt liquid

How to fix this problem?

How to I made calibration 35ppt liquid:
I took 965g of osmosis water. Plus 35 g of NaCl. Mixed it.
optical refractometer shows 35ppt solinity

[Vinny]

When you calibrate the conductivity sensor it is important to make sure the temperature of the calibration fluid is the same temperature of the tank. When you go through the calibration steps, you will have the option to use either the temperature readings from the temperature probe or manually enter the temperature.

[progman]

yes
I put a bottle with calibration liquid inside tank's water ( but no mix with tanks water ofcource ) and wait a few minutes for balance of temperature
and make calibration after that

[Vinny]

If all the calibration steps were followed correctly, then the reading being given by the conductivity probe is correct.

It is not advisable to compare the readings from a refractometer to the readings of a lab grade probe. The conductivity probe will provide you with more reliable readings despite calibrating the refractometer.

[progman]

Calibration process:
I put bottle with calibration liquid inside samp. And waited 1 hour. Temperature of calibration liquid is equal temperature of tank water and equal 26.5^oC

1. Cali. tolerance ( I choise 1 )
2. Calibra. value 2 ( I set 53.0 mS because I have 35ppt solinity liquid )
3. Temp. - Sensor 1
4. Temp. of ca. fluid ( I set 26.5 - the temperature of tank water )
next two measuring in the air and in the calibration fluid
5. Save

after that computer show 35ppt for calibration fluid and 31.5 ppt for tank water.
optical refractometer shows 35ppt for both cases.
Fluval Sea Hydrometer shows 35 ppt for both cases

I took 5 liters of tank water and added sea salt. Now computer shows 35 ppt but optical refracotemeter shows 40ppt!!!!!
How to solve it problem? Computer or sensor lying. Too big lying.

[Vinny]

If the probe is reading 35ppt in 35ppt in the calibration fluid, then the probe is functioning and 31.5ppt is the correct reading.

[progman]

Do you mean that optical refractometer may show very incorrect data?

[GazzMan]

Also, make sure when you hold the sensor in the air, you dry it first, it has to be completely dry.