You don't add aquarium salt to any tanks. Why would you? Look at the reasons you might need to use salt (as in NaCl) in an aquarium:
1. Combat acute nitrite poisoning where water changes alone aren't equal to the problem - ordinary table salt will do this.
2. Treating protozoal infections like ick - a/a
3. Creating brackish water conditions - for this you need marine salt (not sea salt either, you need the stuff the salty guys use, just less of it).
No place for aquarium salt. It's a con trick, built on a number of myths:
1. Fish need "essential electrolytes". Well, they do. Do you need "aquarium salt" to provide them? Nope. Most tap water is already higher in these electrolytes than the fishes' natural waters. Where it isn't, you'll be using rift lake cichlid salts or marine salt anyway (see "Brackish" below).
2. Table salt contains harmful additives. It contains additives, but these are at tiny levels. You'd pickle the fish in brine before you gave them iodine poisoning (or whatever the current "scare" additive is).
3. Salt acts as a prophylaxis against disease. It might, but only by osmotically stressing the fish the same way as it does the potential pathogens. Really, this makes as much sense as taking two paracetamol every day in case you otherwise get a headache. Not usually considered sound medical practice.
Add to this some mystique by not actually listing the ingredients (this is because it's either plain NaCl, or boring old sea salt) and bang - a big moneyspinner for the shops.
Just don't get me started on the similar pH mythology and the lucrative industry that's hanging on the back of that.