For those of you that THINK that the salt is what is healing the wounds or helping your sick fish; could it actually be the frequent water changes you do when your fish get sick?
The salt myth has been around almost as long as the hobby itself. It goes like this ... "You should always add salt to your tank water because it reduces stress, adds electrolytes, improves gill function, speed disease recovery and more."
The quantity of salt you are told to add, seems to vary with the poster and the local mythology, but generally is on the order of one tablespoon per five gallons. This advice seems to be given with no questions asked about water hardness, species of fish kept, presence or absence of live plants, or even water volume of the tank.
The "use salt" prescription is presented as one of the great revealed truths about captive fish husbandry, it's universal and it's rarely if ever qualified or restricted. IT'S NOT BASED ON SCIENCE. In fact, it goes against many of the principals of aquatic biology as we know them.
The statement that "salt helps fish regulate their osmotic balance" is patently ridiculous! All fish are different in this regard, depending on where they live. Some species are native to "soft water/low dissolved solids" habitats while others inhabit hard and alkaline biotopes with high salt concentrations inherent in the water. The species inhabiting these very different environments have developed metabolic processes which take advantage of the specific chemistry of that water. To add salt in the misguided attempt to "help regulate osmotic balance" may actually upset that very balance you are erroneously trying to help.
Does adding salt reduce stress? does salt reduce YOUR stress? Have you EVER asked your fish if they feel better? Of course not and there's no evidence that it does. In fact, in many species of fish it may actually increase it.
Salt adds electrolyte? salt is sodium chloride, period. Yes, those are "electrolytes" but unless you have extremely soft water, you can be certain that it already contains both sodium and chloride and a host of other ions as well. Do your fish need more? what evidence is there to support this "theory"?
Your fish are much better served by leaving them alone and allowing them to regulate their own osmotic balance ... something they have been doing without your help for thousands of years.
The idea that salt is a tonic for fish when it is kept in fish tanks at moderate levels (~ 1 tablespoon per 5 gallons) needs to be taken with a "grain of salt". If your fish are the most commonly kept community fish such as tetras, corys, angels or even the rasboras and most anabantids, these are fish largely from soft, acid, low-TDS (total dissolved solids) waters. The average tap water in the U.S and Europe is at least moderately hard and alkaline and is certainly not improved by increasing the "salt" concentration ... that very thing in which our water already differs most from the natural waters of these fish. Certainly many of these fish adapt well to our local water conditions and I am an advocate of adapting non-breeding fish to local conditions. This is far better for both fish and keeper than constantly battling see-sawing water parameters. Acclimation to your tap water is one thing .... making your water worse than it already is by adding salt however, is quite another.
The prophylactic use of salt to avoid common pathogens and parasites of fish by keeping some level of salt in the tank is also fraught with difficulty. True, the use of salt, usually accompanied by increased temperature, has been known to be an effective treatment for one of the most common ectoparasite, which beginning aquarists encounter ... Ich. However, only the free-swimming form of this parasite is treatable. Neither the fish-embedded growth phase, nor the encysted multiplication stage that rests on or in the substrate is readily attacked by salt or any other medication. Thus prophylactic treatment is useless as it makes little sense to treat a non-infected tank on a chronic basis. Further, any treatment for parasitic infestation is a "medication" and thus the use of salt differs little from the use of any one of the other available Ick medications available at any LFS. The biggest difference in my opinion though, is that of all the medications available, salt is probably the least effective by comparison. As far as the use of salt to prevent bacterial pathogens .. BUNK!
Another fallacy is the addition of NaCl for livebearers. These fish as a group are native to estuarine environments where the waters are likely to be hard and alkaline at least and may even be brackish. The addition of sodium chloride (i.e., "salt") does absolutely nothing to match these species native waters since salt as comprises only a small portion of the total "salt" concentration -- the more significant elements are calcium, magnesium, potassium, boron and silicate salts.
It's important to note that the term "salt" isn't limited to sodium chloride. Calcium and Magnesium salts of carbonate, silicate, phosphate and borate are actually more important to the biology of brackish water fish. If your water is at least moderately hard (GH and KH 8-12) then the addition of some NaCl will do no harm. On the other hand if your water is soft and acid the addition of sodium salt will do little good. You need increased buffering capacity as much as the addition of minerals to the water and NaCl alone does absolutely nothing in this regard. You will need to add crushed coral or aragonite, both of which are primarily calcium carbonate salts, in addition to 'salt' as sodium chloride or better still, use marine salt mix which contains the whole range of cations and anions (positively and negatively charged ions, such as Na+, Ca ++; Cl-, CO3--) found in the sea. This will adequately buffer your water and more closely match the native waters of most live bearers in question.
In a nut shell, "salt" is an old myth that needs to be poured down the drain.
lus1: 
