refractometer
 

I started this hobby with a coralife deepsix hydrometer (testing salinity) but was always worried with my water changes if I was getting accurate readings. With my last order from J&L's I purchased a refractometer. One thing I found out was that the hydrometer was consistently accurate but they just put all their numbers in the wrong spots. It was reading -.004 to -.005 off the refractometers reading. I would recommend to anyone that has only a hydrometer to test it against a friends or LFS refractometer.
Kevin

I agree with Kevin Here... Mind you my hydrometer would have trouble getting the same reading a few times in a row. It was always diligently cleaned WITH RO/DI water right after use to avoid salt buildup, but I still had problems with it. The purchase of my refractometer was probably one of my most... relieving purchases.

Chris

-Edit: Another problem with hydrometers is they are temperature corrected to 15 Degrees Celcius - This causes a problem with the readings we normally get with our tanks. Refractometers do also come calibrated to a certain temperature, but do not have as much difficulty with varying water temperature, and also can be calibrated to the correct temperature (Mine is to about 77/78 Degrees).