Neptune Salnity probe vs Red Sea refractometer

[DS204]

Hoping someone can please help me!

I've been keeping a small saltwater tank for almost a year and have been using the Red Sea refractometer. I regularly calibrate it using RODI water as mentioned in the instructions. I keep my tank around 32ppt salinity.

When I setup a new Red Sea aquarium I went all out and got a neptune controller. I finally calibrated the salinity probe last night and placed it in my sump. Much to my surprise, the salinity reads much higher than I expected at 37ppt.

Now I'm wondering, which is accurate? I read a little bit online about the difference between the two and that one uses conductivity and the other uses light refraction.. but, to the average joe reefer like me - which should I be relying on as accurate? It surprised me to learn that I've been keeping my tanks super salty, when I thought I was actually at 32ppt!

 

[Silver14SS]

Without comparing them to a standard you won't know which one is right. I recommend calibrating the refractometer in the range you'll be testing instead of 0.

@Randy Holmes-Farley has a great article on how to make a standard at home.
http://reefkeeping.com/issues/2004-06/rhf/index.php