Go to Home Depot. Buy 50 pound bag of Rock Salt for $3.69
I rarely use salt anymore unless fish I get had some stress getting here.
Salt I think is used to much.
WC's, filters cleaned, tank walls cleaned is the best line of defense for almost everything.
BTW. I wish i was the one who thought of Aquarium salt. LOL!
Whom ever that was they were a marketing GENIUS!