Been keeping FW fish for over 35 years and never needed to add any salt. How are you going to keep up with your salinity in the percentages that would be safe? There are all kinds of old wives tales out there that say to add salt, same thing for koi and gold fish ponds etc...keeps ich away, chases parasites off, aides osmosis etc etc etc. Keep the salt out of the community tank and only use it in a QT tank if the need arises. It does not take much salt to kill some freshwater fish BTW. IIRC I read about a test as to lethality of salt with various tropical aquarium fish, and some species of catfish and gourami, and tetras kicked the bucket with just a very low percentage. Some fw tropicals can be acclimated and kept in brackish to saltwater just fine..Guppies and platys do exceptionally well in a 1.021 or so sg........Salt is also gong to kill any live plants if you have any.
Keep the salt for the marine fish or for use in the kitchen.