If you are asking about the fish listed in your sig, I would say they are fresh water fish. Do you have any live plants in with your fish? By adding salt you are increasing the TDS of the water. I don't think you are doing any harm but, what will you do when salt is no longer a choice for a type of medication? Do you have a problem with high levels of nitrItes, because this will relive nitrItes poisoning.