Quote Originally Posted by DarkHorseMBA View Post
Ok did my own test and here's the scoop.
Used a reference liquid from fosters and smith, read 35ppt perfect.
Used distiller water and it read 0ppt.
So distilled water works fine no need to spend $8 on calibration fluid.

DarkHorseMBA
You should use both. It can still be off when just using distilled water. Here's a URL that better explains why:

http://reefkeeping.com/issues/2006-12/rhf/index.php