Hooloovoo
New member
I need some help figuring out how to accurately determine my tank's salinity. This is for a new tank with no livestock added yet. I have an Apex Controller with conductive salinity probe, and a refractometer. I would tend to trust the refractometer more than the conductivity probe, but I am having some concerns about the calibration of the refractometer.
The refractometer is a JBJ CScope that I purchased over at World Wide Coral's brick & mortar location in Orlando. It's the same model they use. The instructions that came with it said to calibrate with distilled water, which I did initially. When I got my Apex installed and calibrated the salinity probe, the results were way off from what my refractometer showed. I tried recalibrating the conductivity probe several times, but its results stayed consistent.
After some investigation, I came across a post suggesting that it was more accurate to calibrate refractometers with a 35 ppt refractive calibration solution, so I purchased some from BRS and recalibrated my refractometer accordingly.
Here is the calibration solution I used:
This brought the refractometer and conductivity probe measurements much closer to agreement, and I was satisfied with the result until...
I took a water sample over to World Wide Corals to have them test it (mainly because I was getting conflicting results from my Red Sea and Hanna Alk tests, but that's another story). They told me that my salinity was way too high. I explained my previous calibrations, and they told me that they alway calibrate to 0 using RO/DI water. They went ahead and checked their calibration using RO/DI while I was there, and then confirmed that their tanks were showing the proper values with this calibration.
Now my question is, should I calibrate to 0 using RO/DI, or should I continue to calibrate to 35 ppt using my refractive calibration solution? My instinct would be that the calibration solution would be more accurate, but World Wide Corals is obviously very successful keeping their corals at a salinity based on measurements obtained with RO/DI calibrated refractomers.
I decided to take a series of measurements using both calibration methods to confirm that it does make a difference.
Here is the reading I get from my display tank after calibrating my refractometer to 0 ppt using RO/DI:
Here is the reading I get from my display tank after calibrating my refractometer to 35 ppt using the calibration solution:
Meanwhile, my Apex conductivity probe reads 35.1 ppt.
The refractometer is a JBJ CScope that I purchased over at World Wide Coral's brick & mortar location in Orlando. It's the same model they use. The instructions that came with it said to calibrate with distilled water, which I did initially. When I got my Apex installed and calibrated the salinity probe, the results were way off from what my refractometer showed. I tried recalibrating the conductivity probe several times, but its results stayed consistent.
After some investigation, I came across a post suggesting that it was more accurate to calibrate refractometers with a 35 ppt refractive calibration solution, so I purchased some from BRS and recalibrated my refractometer accordingly.
Here is the calibration solution I used:
This brought the refractometer and conductivity probe measurements much closer to agreement, and I was satisfied with the result until...
I took a water sample over to World Wide Corals to have them test it (mainly because I was getting conflicting results from my Red Sea and Hanna Alk tests, but that's another story). They told me that my salinity was way too high. I explained my previous calibrations, and they told me that they alway calibrate to 0 using RO/DI water. They went ahead and checked their calibration using RO/DI while I was there, and then confirmed that their tanks were showing the proper values with this calibration.
Now my question is, should I calibrate to 0 using RO/DI, or should I continue to calibrate to 35 ppt using my refractive calibration solution? My instinct would be that the calibration solution would be more accurate, but World Wide Corals is obviously very successful keeping their corals at a salinity based on measurements obtained with RO/DI calibrated refractomers.
I decided to take a series of measurements using both calibration methods to confirm that it does make a difference.
Here is the reading I get from my display tank after calibrating my refractometer to 0 ppt using RO/DI:
Here is the reading I get from my display tank after calibrating my refractometer to 35 ppt using the calibration solution:
Meanwhile, my Apex conductivity probe reads 35.1 ppt.