Thought this was interesting. From another forum I was reading. My aquacraft 35ppt calibration read 1.030 in the cup. Quote:
Originally Posted by MarksReef View Post
Do you have any 35 PPT calibration solution to test it with ?
Does reading in SG make it any closer?
Calibration solution is a tricky animal because you need solution designed for the instrument you are calibrating. Solution that reads 35ppt on a refractometer may not read 35ppt on a conductivity probe like the icecap. A calibration solution for a refractometer may use something other than sea salt that has a refractive index of 35ppt, but doesn’t have the same conductivity as seawater. Likewise, a solution designed for a conductivity probe may not have a refractive index of 35ppt. So when you are looking at calibration solutions you need to make sure the solution is designed for the instrument you are testing.
Now, that said, I do have an old bottle of pinpoint 53ms calibration solution, which is designed for the pinpoint conductivity probe. Pinpoint has stated that this solution is very close to seawater and it should read 35ppt on a standard refractometer as well.
Unfortunately, like I said, the solution is very old, so I’m not sure it can be trusted. When I tested with that solution I got a reading of 34.5ppt on the icecap probe and 40ppt on my Milwaukee refractometer. Again, I’m inclined to trust the Milwaukee refractometer here as the solution is several years old and may have evaporated, which would cause high readings. The reading on the Milwaukee refractometer also is much closer to my standard refractometer and my apex conductivity probe. I have a hard time believing that the three devices which produce very similar measurements are all off.
Reading in SG doesn’t make a difference. Like all conductivity probes, the icecap probe actually reads in ms (millisiemens) and just uses a mathematical calculation to convert to SG and PPT. If one is low they are both low.
