Petsmart and Petco use salt in their tanks. The Petco I had in Maryland used salt in all their tanks - display tanks and the tanks that the fish to be sold were in. I would here the sales associates tell new buyers to buy the aquarium salt becuase they need to have salt in their tanks. They only time I have ever put salt in my 55 gallon was when I had an ick breakout. As soon as the ick and waiting period were over, the salt was slowly gotten rid of through water changes.