Salt promotes the slime coat to develop which helps prevent bacteria from getting into any sores or other injuries. Na ions irritate the skin and cause a slime coate to form, CL ions bond with the receptors in the gills more readily than NH4 does, which is why "salt" is listed as being beneficial to fish.
Finrot is almost always a sign of bad water quality, in his case uncycled tank.
I'd test the GH and KH in the tank and if the GH/KH is to low either add crushed coral to the substrate, or do something like the salt mix above. GH should be 7 or higher and KH should be 10 or higher for most African cichlids. The baking soda raises the KH, the Epsom salt raises the GH, the marine salt raises both a little bit along with adding Na and CL ions to the water.
Downsides when doing water changes:
Crushed coral, a large water change causes the PH to drop and come back up gradual. So requires smaller, but more frequent changes.
Salt mix, you have to have it on hand and mix it OUTSIDE the tank in proportionate amounts to what you remove.
Robert