Replacement salinity probe reading high

[timmcq]

Roberto,

I've installed the replacement probe and get high readings.

Each time I attempt to calibrate I get similar results. When calibrating, as the probe sits in 35 solution, the numbers fluctuate around 2768, not in the 3000s, like before. After calibrating, my tank reads 421 on the controller. My water is actually right around 35. I continually check this with my refractometer and hydrometer.

This probe looks different than the other. Is there anything else I need to do either in the code or calibration?

Tim

[rimai]

Yes, the probe is different, but the calibration should show 35ppt when you finish the calibration.
If it is not, something didn't do right with the calibration.

[timmcq]

Roberto,

I have tried several times. I recalibrated and still get high readings. You can see in my charts that the salinity reads around 38-41. Could I be missing something in my code? My probe is not fully submersed? Should it be?

Tim

[timmcq]

During calibration, the numbers fluctuate around 2930.

After calibration the probe (still in 35 solution) reads 357 - 361. Much closer. Placed in tank water it reads 390. From this, I would assume my water is too high. So, I check with a hydrometer and calibrated refractometer. Both read 35 dead on.

I do think the probe is reading high, but that doesn't explain the range of results I am getting. I still think that I may be doing something wrong.

Is it worth looking at my code?

[rimai]

Calibration needs to happen at the exact same temperature of your tank water. 1 degree of temperature can swing the salinity up to 2ppt.
Salinity is based on electrical conductivity, which is highly dependent on temperature.
If calibration doesn't occur at the exact same temp, you will see discrepancies.
What happens if you calibrate with your tank water, since you are positive that your tank is 35ppt?
That's what I do. I calibrate mine with the probe in the sump. This way I ensure same temperature. You just need to be certain the tank water is correct. That's all.

[timmcq]

That makes sense. I will do that, as well as bring my 35 solution to tank temp.

I am also having a friend double check a sample of my tank water for salinity.

[timmcq]

I brought the 35 solution to tank temp. Now I'm getting 35.8, 36.0, ...

Much closer. I will work on it.

Thanks!

[timmcq]

35.0 - 35.2. Perfect

I just allowed the 35 solution to float in tank for a while. I didn't realize that temp had such an impact.

Thank you Roberto!