Salt bath dose is 1 tsp per 1 gallon... so I'd got 1/2 tsp per gallon? I usually eye-ball it. If he has never had salt in his water before you may want to go light and supplement with salt baths (but I'd only do the baths if you see any actual redness or rot). Someone else may want to chime in with a better suggestion? This is what I have been doing in my guys' water while their tails heal, but don't feel confident enough to say that it is 100% right.
Here is a good thread on salt baths:
You may want to look into Indian Almond Leaf (via ebay or aquabid). These are found in their natural habits and a couple of my guys have really calmed down since I started using them (plus they like building bubble nests under them :)