Aquarium Salt, Aquarisol, Melafix, Bettafix, Tetracylene, Maracyn1 & 2 are for fin rot.
Any of those can be used in a 1 gallon, whether tablet form or liquid.
Tablets
Liquid
The whole syringe...1 tsp (5ml)..........treats 10 gallons
3/4 the syringe.......3/4tsp (3.75ml)....treats 7.5 gallons
1/2 the syringe.......1/2 tsp (2.5ml).....treats 5 gallons
1/4 the syringe.......1/4 tsp (1.25ml)...treats 2.5 gallons
1/5 of 1 ML ............(.20ml)..................treats 2 cups
So to treat 1 gallon you need 3/5 of 1 ML.
3/5 of the 1ML section = 3rd tick (.60ml) = treats 1 gallon
Aquarium Salt should be dosed as 1 Tablespoon to 1 gallon of water.