Calibration Confusion, What’s Going On?

JCas06 · Jan 29, 2023

So I just purchased the new Hanna Marine Monitor that has a PH probe and a Salinity/Temp probe. The unit continuously displays the above and uses temp to accurately calculate it’s readings. I hooked the unit up and followed the instructions on how to use the included 7.1 ph solution satchets and 10.1 ph satchets to calibrate the probe. Then I calibrated the salinity probe with the 35 ppt salinity solution. Put everything in the sump and got a ph reading of 8.2 and salinity of 37.1 ppt. Those were higher than expected and so I checked the salinity with my refractometer which I calibrate with ocean water as I live in South Florida and we get clear Caribbean water which I also use for water changes.

I found my salinity was 35 ppt on my refractometer. I also happened to order some bulk reef supply calibration solution so I put that in my refractometer and it read 30 ppt. So I adjusted my calibration on the refractometer to the bulk reef supply standard and tested my tank water again which now showed 40 ppm! I’m totally lost on what is correct here. The ocean water sample cannot possibly be 40 ppm I collected it a couple miles off the coast in 400 feet of water. If anything an ocean water sample has the possibility of being under 35 ppt due to inlets releasing brackish water out into the ocean and fresh water has a tendency to float on top of salt water. What salinity reading should I trust?

Now on to PH. The Hanna marine monitor probe read 8.2. I also tested with my Hannah alkalinity checker and it gave a reading of 7.6. So I calibrated the Hanna alk Checker with 5e Hanna 5.1 calibration cuvettes and the checker nailed it at 5.1 ph. So I have two different Hanna machines that are calibrated reading in my opinion a widely different number. How can this be?

Tank is 100 gallon mixed reef tank

Thanks,
Jason

DanyL · Jan 29, 2023

Seawater like you already mentioned is fluctuating on the surface, so I don't think it'll be a suitable calibration solution.

Have you tried moving the probes into a cup of water and comparing the results?
These probes are measuring conductivity which can be influenced by other electronic devices found inside the tank, by isolating this variable you may find where the culprit is.

Another test I would do is to measure the both calibration solutions.
Both are supposed to be at a certain set point, and thus when calibrated properly should show the expected result.

Another thing to note is that calibration solutions can go bad from varying reasons, so this is a possibility as well.

gbroadbridge · Feb 8, 2023

JCas06 said:
Now on to PH. The Hanna marine monitor probe read 8.2. I also tested with my Hannah alkalinity checker and it gave a reading of 7.6. So I calibrated the Hanna alk Checker with 5e Hanna 5.1 calibration cuvettes and the checker nailed it at 5.1 ph. So I have two different Hanna machines that are calibrated reading in my opinion a widely different number. How can this be?

pH and Alkalinity are not the same thing ...