It's the brineing that fish don't like. When the salt disolves you can see waves in the water. Those waves are what you call brine. as in "Brine Shrimp" yes. This fluctuation of ionic atoms breaks down the gills and can hurt the fish. Predilute 25teaspoones of salt in a gallon of hot water. Do a water change fill the tank back up and while putting the water in mix the salt water. This will make it go in evenly.