black Friday $25 refractometer

[Pufferman]

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

[LRU]

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.

[Pufferpunk]

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

[Pufferman]

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.

[Pufferpunk]

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.