Conductivity - cannot calibrate accurately

[ergo]

Hello

I finally received my conductivty probe yesterday and calibrated it, then put it in my tank. According to the probe my salinity was waaaaaaay low. I added salt to bring it uo t0 1.023 on the probe, and then checked it with my refractometer, which read 1.030:eek:

I have re-calibrated the refractometer today, no change in the reading. Thought I would also re calibrate the probe, and it cannot get near the 50mS which the solution is. I have tried 3 times this evening, the closest has been 44.9, a difference of greater than 10%!!! It does read zero when in the air.

The calibration fluid was 22 degrees, which I entered when prompted - is this why it never got to 50mS (as teh solution is 50mS @ 25 degrees)

I am now in a quandry, it is possible that my SG is way too high now, but then again maybe not!

Any suggestions please?

[stevew@reefdreams]

Our posts crossed in the night!

Take a look at your other thread where I have tried to shed some light on the differences.

http://www.ultimatereef.net/forums/showthread.php?t=313849

Hope that helps and is understandable.

Steve

[ergo]

thank you for your lengthy and detailed post - a considerable effort you put in there - but I am still confused!!

My probe read 44.5mS at a temp of 21.5 degrees during the calibration process. According to the link in your post, this has returned a value of 31.3 ppt

Now it is in my tank, it is reading 50.8mS at a temp of 27.8 which returns a value of 31.4

Admittedly these two readings are very consistent, which is a bonus, but do I dare add more salt?!

[stevew@reefdreams]

Did you have the temperature probe and the conductivity probe in the calibration solution at the time you calibrated?

It is much better to float the solution bottle in a sealed bag (squeezing the air out of the bag first) for an hour in the sump and then do the calibration. That way you are working at the temperature you are going to be measuring at rather than 6 DegC different as you have.

Ignore the salinity conversion, just work in conductivity as my post recommends, you are aiming for 53ms.

Steve

[ergo]

Steve

Really sorry to drag this out. I have followed your suggestion - I think it is resolved but wanted to run the results by you:

tank temp 28.6 - conductivity reads 53mS

50mS/25 degrees calibration solution @ 28.6 degrees reads 49.6mS

Am I all sorted calibration wise?

Assuming that the reading from the probe makes an adjustment for temperature, my reading of 53mS is on the money - I am right?