We talking about salt for fresh water, cause I know if I add some aquarium salt in my arowana feel more active and eat more.
For you guy how much salt of home depot that you use for each gallon of water?
I am sorry to say this but you are practically wasting your time and money just by adding salt unnecessarily in your setup. I have kept freshwater for a long time and never added salt in any of my tanks except the marine setups (which of course, is understandable in itself).
If your fish seems to perk up because you add salt in it, perhaps we should look at your water parameters as the possible culprit for its unusually lagging behavior. What are your ammonia, nitrite and nitrate? What test kit do you use? If your tank has high level of nitrite, then perhaps your tank is not receiving adequate maintenance. In this case, you should look at your feeding schedule and maintenance and see where it needs to be improved to keep your ammonia and nitrite in check (assuming your pH is not on the high side that ammonia becomes extremely toxic). The salt itself can neutralize nitrite temporarily when it intoxicates your fish but if your nitrite keeps elevating itself, then something is wrong with your tank's environmental conditions.
Adding salt on a permanent basis perhaps may help some fish but in the long run, you also risk producing resistant strains of parasites particularly ich/white spot disease that treating the fish becomes quite a task in which case, you will end up resorting to powerful medicines that may also potentially kill your fish.
