Hi Jim,
I use either pond salt or cooking salt. This should be used at a rate of 1\2 Oz per gallon of aquarium water, at this rate it is very effective, cut back on your usual feeding whilst treating, the salt can in some cases knock the bio filter back slightly so by not feeding quite so heavily helps to keep a nice balance. A good tip is to use half the dose the first day and the other half the second, again reduces the chance of upsetting the filter by using this method.
Make sure the salt is fully dissolved before adding to the aquarium Jim, you can put the salt in a pillow case and hang it in the tank somehow near the flow and let it naturally disperse. Salt unlike chemicals will not break down so will stay in the tank at full strength until such times you do a water change, 5 to 7 days should see significant improvement.
Note
When you weigh this out it will look an awful lot of salt....always does! but at this strength its perfectly safe for all the other fish also.