bonebrake
Active Member
I just wanted to post this for everyone's edification because I recently learned this myself.
Only a lab-grade quality refractometer can get away with being calibrated with distilled water or RO/DI water. The cheap ones we use in this hobby (less than $100) can still be inaccurate when you use distilled or RO/DI water to calibrate. For example: say each increment is off +/- 0.0001. You would think this would not be a big deal, but when you calibrate at 1.000 s.g. and then go all the way up to measure your saltwater at an s.g. of 1.025-1.026 that +/- 0.0001 per unit of 0.001 is now a total margin of error of +/- 0.002. So your saltwater could actually be anywhere from 1.023-1.028!
It turns out I had been keeping my water at 1.027-1.028 all of this time when I intended to keep it at 1.025-1.026. A month ago a reef buddy of mine told me about all of this and he had a standardized solution that has an s.g. of 1.025 at room temperature of 72 *F and I calibrated my refractometer to that so it would be right on.
Does it really matter if your refractometer is off? No, but it is nice to have it be as accurate as possible so you're at least keeping your s.g. where you think you are.
:joy:
Only a lab-grade quality refractometer can get away with being calibrated with distilled water or RO/DI water. The cheap ones we use in this hobby (less than $100) can still be inaccurate when you use distilled or RO/DI water to calibrate. For example: say each increment is off +/- 0.0001. You would think this would not be a big deal, but when you calibrate at 1.000 s.g. and then go all the way up to measure your saltwater at an s.g. of 1.025-1.026 that +/- 0.0001 per unit of 0.001 is now a total margin of error of +/- 0.002. So your saltwater could actually be anywhere from 1.023-1.028!
It turns out I had been keeping my water at 1.027-1.028 all of this time when I intended to keep it at 1.025-1.026. A month ago a reef buddy of mine told me about all of this and he had a standardized solution that has an s.g. of 1.025 at room temperature of 72 *F and I calibrated my refractometer to that so it would be right on.
Does it really matter if your refractometer is off? No, but it is nice to have it be as accurate as possible so you're at least keeping your s.g. where you think you are.
:joy:
