The Importance of Refractometers

[jap1]

Well today I went to Wolf Reef to give them my sand sifter that I decided against keeping. While I was there I asked Ed to test my salinity with their refractometer. Well lo and behold it read 1.031!!! I have a deep six hydrometer which I have always been good about rinsing out with fresh water after every use. My hydrometer has been reading 1.025 which I always thought was healthy. That's .006 off! Well atleast everything in my tank seems healthy, but I need a refractometer. I sure hope I win that raffle!

[NaCl_H2O]

The swing arm hydrometers are garbage IMO. I have had several and none gave an accurate SG reading. Also, salinity monitors (e.g. pinpoint) will also drift over time and can fail. Refractometers are probably the best & easiest, but also require regular calibration and checking against a stable source. Just calibrating to 0 SG really isn't enough. I use a floating bulb hydrometer to check my refractometer after calibration.

I was in CB a few weeks back and Mark was checking SG for a customer. He calibrated both his & customers refractometer and they were .002 apart. Then we pulled out a floating bulb hydro off the shelf, and got yet a third reading. Which one do you trust?

IMO, the floating bulb is the only true tusted source, but you need to make sure the water sample is within the temp band on the hydro, and used in calm water - I put a sample in a graduated cylinder for my floating bulb hydro check & compare to the refractometer after I calibrate. I do this about once a month.

[TheOtherGuy]

LOL - I remember that Steve! Have gone through similar situations several times since then too!

Even refractometers can be misleading.

[bigdscobra]

how often should you need to recalibrate your refractometer??

[cpreefguy]

how often should you need to recalibrate your refractometer??
It depends on the refractometer. I finally ordered one (after ~5 years in the hobby), it was one of the more expensive ones that came calibrated from the factory, and it says it rarly needs to be recalibrated.
Recalibrating in simple though, the refractometer should come with a tiny bottle of "Ultra Pure Water", you drop it on the prism and set it to zero with a supplied screwdriver.
If you dont have one,
GET ONE!!!
Theyre not that expensive and the swing arms are too inacurate for comfort IMO.

[NaCl_H2O]

I probably cal mine every 30-60 days using RODI. Usually only very minor adjustments are needed. Before you cal, make sure the glass and cover are rinsed well with RODI to remove any residual salt.