I think a bit of clarification may be in order. The "myth" being referred to is the idea that aquarium salt should be added to freshwater aquariums (at whatever amount of salt per however many gallons of water) because some amount of salt in the water is good for freshwater fish.
the only thing salt is good for that I've seen
1. Getting rid of Ich
2. Repairing any wounds on the fish
through my ridiculous battle with ich one of my bigger loaches got a hole straight through his dorsal fin...nice sized one too
that night I started dosing the salt (after 1 month of treatments with no success) 1tsp per gallon and the next morning the hole in the loaches dorsal fin was completely repaired...not even a sign of it being there
so it is beneficial depending on what you use it for
but to add it to a freshwater tank for the sake of it...I don't see it necessary whatsoever
I've even talked to petsmart employees that say they don't use salt in any of their freshwater tanks (even though if you look really closely you can see the small sticker that says they use aquarium salt in all their tanks)
I buy a 4lb box of pickling salt for $1.58 and keep it on hand for ich/etc. It is plain salt, no additives and works exactly the same as "aquarium" salt.
