Fritz has been making pre-dissolved salt for years under their “Pro” line and selling tons of the stuff. It’s popular with larger customers (fish stores, wholesalers, etc.) but we haven’t seen it in consumer friendly packaging. Quick Change is now available in 64oz or 1 gallon sizes and is designed for use in marine, reef or brackish aquariums. You’ll need to mix the quick change concentrate with fresh water before adding it to your tank. The salt concentrate contains essential major, minor, and trace elements, plus extra magnesium and calcium. The 64oz version retails for around $10 and the one gallon size comes in around $15 even. The 64oz variety makes about 4.5 gallons of saltwater and the 1 gallon makes around 9 gallons.
Image courtesy of Foster and Smith