Hydrometer vs Refractometer
 

Yesterday I bought a Sybon Refractometer at Red Coral and today... I am horrified!
I have been using a Coalife Deep Six Hydrometer and my readings have been between 1.025 to 1.026 and have been so for about 4 months with very little change ever since I bought a Tunae ATO.
I messured the Specific Gravity with the new Sybon, my water tested out at 1.029! :eek: I tested the purified water sample that came with it to ensure it was calibrated correctly at the factory (it was).

Having the SG at this level is not fatal (obviously), but is probably partially responsible for the slower growth of some of the corals. I will lower the SG levels to 1.026 over the period of a week or more.

I find it amazing that there can be a .004 difference between these two instruments.

I would be interested in anyone with similar experiences.

I have the exact same hydrometer as you and bought the exact same refractomter as you yesterday as well. My salinity is .004 higher as well. Will be adding fresh water slowly now...

Double check your refractometer before you make changes. Pure water is NOT a good calibration standard for these things. Read this:

http://www.reefkeeping.com/issues/2004-06/rhf/index.php

.004 of a difference is normal between a hydrometer and a refractometer. That why refractometers are recommended. A friend of mine's hydrometer was out by .008, that is why hydrometers are not very reliable.

hydrometer vs refractometer
 

just a quick note .those refractometers have to be calibrated did you get calibration fluid? you can do it with ro water. we use swc refractometers here. great results.dan

correct me if im wrong as i dont have a refracto and i have used a friends to find out my hydro is out .0015 aprox. but are you not supposed to use distilled water to zero in a refracto?????/

Yes, distilled/RO/RODI, is what I've been told to use and RO is what I've used for calibration purposes.

hdro vs refractometer
 

yes you can use ro water to calibrate remember ro water is at 0 so look in your refractometer if its not at zero adjust the screw to bring it to 0 been doing for 10 years.dan

hydro vs refractometer
 

we suggest in the future have the store where you buy your refractometer calibrate it for you hope this helps.dan

Your refracto should have come with calibration fluid, I got mine at Red Coral too, same one, and mine came with it.