Lots of debate still going on with the aquarium salt......it stems more from the old timers like me...lol.....many years ago before we knew better and before more scientific research, updated filtration and general knowledge of water...we relied on sodium chloride to help keep our fish alive.....now with better filtration and knowledge we have found that salt is not needed and can be bad/harmful in some cases especially long term use.
Aquarium salt (sodium chloride) is a great product to use short term for treatment when used for the right reason, dosage and duration....long term use can cause resistant issues and kidney damage with incorrect use
Long term use can be risky especially if you do have a problem and you need it for a treatment....it may not work......and you may start to see bloat problems for no reason with some fish that have been kept in salt long term and this is usually due to kidney damage/system shut down due to long term salt.
Some fish are more tolerant to long term salt and other are not and with some species the use of small amount can be deadly
With brackish fish it is best to use marine salt like what is used for saltwater fish since it has more minerals that the brackish fish need.