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Dissolve 1 teaspoon per 1 gallon (4 L) of water in a small amount of tank water separately and then add the mixture to the tank. Leave the salt in the freshwater aquarium for 10 days. Salt disrupts the fluid regulation of ich and also helps develop your fish's natural mucous or slime coats to protect it from ich parasites. Combine salt with heat to further effectively kill off ich.  Use aquarium salt that is specifically design for fish and not table salt which is not iodine-free. Never use medication along with salt and heat as the salt and medication can react and restrict oxygen within the tank. Change 25% of the tank water every few days and only add the correct amount of salt to water taken out. However, if the treatment is over, do partial water changes but don't add anymore salt. Partially changing the water everyday can help remove some trophonts and tomites from the tank and also add oxygen to the water. Be sure to use treated water so the extra chlorine won't stress your fish or agitate your fish's wounds. If water changes stress your fish, decrease the amount of water or frequency that you change.

Summary:
Use aquarium salt to treat ich in freshwater aquariums. Do 25% daily partial water changes.