Sorry to hear you've been given bad direction. I'd be interested to hear which LFS said that, you can PM me if you're too shy to say publicly.
Throw the hydrometer in the garbage. You'll get a more accurate reading by dipping your finger in and tasting the water IMHO.
Get a refractometer tomorrow. It's a basic staple in keeping a salt water aquarium... but you know this.
What brand of salt was it? Generally speaking, it's about half a cup of salt to one gallon of RO/DI water. So for 20 gals you should have used about 9 cups, then measured salinity and adjusted from there.
Good luck.
|