APEX Salinity Calibration Issues

rbraunberger · Jan 22, 2017

I was calibrating my APEX salinity probe with the Apex 53000 solution. I finished the calibration and ended up with a ppt of 31.9. I checked that up with my Milwaukee digital refractometer and it is reading at 35 ppt (1.026). I do have a temp probe attached to the salinity module...how do I get them to match?

Thanks!

Scott.h · Jan 23, 2017

Float the bag of calibration solution in the sump next to the temp probe. That will make a difference making sure they are at the same temp while calibrating.

Btw, my glass bobber, apex, and refractometer all very slightly. I trust my refractometer over all. And I use the apex more less in case my ato goes nuts.

rbraunberger · Jan 23, 2017

Scott.h said:
Float the bag of calibration solution in the sump next to the temp probe. That will make a difference making sure they are at the same temp while calibrating.

Btw, my glass bobber, apex, and refractometer all very slightly. I trust my refractometer over all. And I use the apex more less in case my ato goes nuts.

I floated the solution for 2 days next to the temp sensor...and I am having a large variation. Digital says 35 after zeroing out, and apex says 31.7. BIG difference

Scott.h · Jan 23, 2017

I floated mine 20 minutes or so and recalibrated over the weekend. It's just a touch low now, but they don't seem to stay accurate. Mine starts low and floats high

micorals · Jan 23, 2017

How old's your Apex probe? I think I read somewhere that Apex recommends replacing probes every 1-2 years.

Scott.h · Jan 23, 2017

Well shoot, they have a one year warranty, and mine wasn't accurate out of the box. I'd be danged if I spent more on another in one to two years.

Salty1962 · Jan 23, 2017

Make sure there are no bubbles in the tip of the probe, it will throw it off

Breadman03 · Jan 24, 2017

I had trouble with mine. It seemed to calibrate quickly, but left me with a reading of about 30. I don't really need it to match and I just left it be until recently. I wasn't too confident because the Apex gave me one reading, my refractometer gave me a different one, and my hydrometer had yet another and the spread was enough for me to doubt all of them.

I revisited the probe setup page on the classic pages and noted the range selections. I changed it from "Salinity" to "High". Bam! Like that, the probe and my hydrometer were in perfect agreement. Mind you, I used Aquacraft calibration solution that claims to be 53ms and have a 35ppt refraction index. Next up is to use Randy's DIY recipe for calibration solution to check my hydrometer.