Btw same risk can also follow digital ones. Drift in any equipment can occur due to its components decaying and changing property over time. My Milwaukee after calibration will read a brand new 35ppt calibration as 36..I calibrate off a friend who has a Milwaukee digital. Calibrated 4 days ago and tested my tank, 35ppt. I just mixed up some calibration solution from the formula in the article posted above and it was exactly 35ppt.
I have a cheap refractometer so as expected, my reading of rodi water was well below 1.000sg.
I see why the red sea would be more accurate and why using rodi is a good way to calibrate it but you're still relying on the equipment to be manufactured without any errors.
Just another thing that needs redundant checks to confirm accuracy. I don't trust calibration solutions anymore, mine was brand new and was off by 5ppt.
Here are some useful recommendations I have used over the years to yield best possible accuracy.
- Use red sea or another one that is made to be calibrated with rodi.
- Have both rodi solution and the refractometer in room temp for 30min minume so both have the same temp. Also make sure you know what the temp range your refractometer is spec'ed for. Every refractometer have a temp range tolerance, make sure your are withen this temp range otherwise refractometer will be out of its temp compensation range.
- add the rodi to the refractometer and leave it for at least 10min.
- now read and calibrate the refractometer.
- after calibration, while clean the lenses and as an extra step you can use a 35ppt solution that you trust to see where you are.
- alwayes rinse the prism es of the refractometer with rodi solution after you use it. Salt creep and leftover salt water will impact the prism
- store your rodi in its package to protect it. Falls and hits on the device can shift the presim and impact its accuracy.
If you want to use refractometer that use 35ppt calibration solution, it's also ok just follow the rest if the comments mentioned above and alwayes rinse the prism after you calibrate using the 35ppt solution.
Oh one last thing, when you wipe the preaim do not use force. Refractometer prism can shift a bit and mess the calibration again.
You see how something as simple as salinity can have so much debate and informations...fundamentals are known to all but definition of these fundamentals are the diffrence between thriving and struggling system.
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