I don't know HOW everyone else here has been measuring or what they are measuring with... BUT I use Instant Ocean salt and and Instant Ocean Hydrometer and I do EXACT 5gal water changes too... Acording to my Hydrometer.... EXACTLY 1 and 7/8ths of a cup will give you a 1.021 spec grav... In my experience.

there is no other salt water people in hinton i know of nd are store is usless here they got nothing 4 salt water

Did the swing arm thing come out of the hydrometer's box thing?

I dropped mine once and thought it was broken, but the pieces do fit back together if none of the pieces have actually broken. Have done this with my old hydrometer before I got the refractometer.

1/2 cup per gallon (Using an actual measuring cup) works out perfect every time for me.

the little tabs that hold it in broke she said she droped it but i think she might have steped on it