Hello Tlay...
Standard aquarium salt is fine for most aquarium fish. "Livebearers", like Guppies, Swordtails, Mollies and Platys will do well with a little and my Corydoras are fine with it. Mollies are really brackish water fish, so they may need a little more. A tablespoon in every 5 gallons of new water is a bit high for most fish and aquarium plants don't seem to do well with this much, long term.
I've kept fancy Gupplies and Corydoras for several years and found a teaspoon, one-third of a tablespoon, is plenty for the fish and with this smaller dose, my plants do a lot better.
Your decision. Experiment with different amounts of standard aquarium salt and see how your fish and plants do.
B