The Puffer Forum

I wasn't sure where to post this but the reviews are great and the price is probably wholesale, I just ordered mine.
http://www.bulkreefsupply.com/refractom ... fluid.html

If the pic is right, it's ATC brand. You can get on eBay for $30 just about any day, but if you have free ship from BRS, a nice find.

That model will vary in accuracy from unit to unit - sometimes linearly, sometimes on a curve. I'd calibrate as close as possible to the point where you're testing (e.g. with freshwater/distilled/whatever instructions say) on the low end if you're doing brackish, or else with the 35ppt salinity fluid if you're doing a full marine tank. That way any inaccuracy is on the other end of the scale.

Great thread on this on 3reefs or somewhere but I can't find it at the moment.

Be sure to get the calibration solution or it's worthless.

It is the ATC brand and it came with the calibrating solution to set at 1.026sg. I'm sure glad I didn't put this tool off because my Instant Ocean Hydrometer was a full .004sg off. I verified by taking a water sample to the lfs and it was dead on with my new ATC refractometer. I did rinse the hydrometer after every use also so I will be warey of any Instant Ocean products for a while. That could have crashed my tank if I had kept raising the sg and the real reading was .004sg higher than I thought.

Perfect! Probably not crash the tank. Mine was off by that much, so my SG was 1.030. Corals did look a bit "off" but looked better at 1.026.