Yes - pop him back with the others as the salt will knock them out and then there's no chance of cross-reinfestation.
I'm going through - or nearing the end of - an ich infestation myself and i just went down to my local supermarket and purchased a couple of packets of sea salt - all free from added chemicals.
Have you got a heater you can use?
The way this works is you quickly add your 1 teaspoon per gallon, then 12 hrs later, the other and then 12 after - the remainder (exactly as Cathy outlined above) and once that's done, then start raising the temp of the tank..... What this does it speeds up the lifecycle of the parasites and then the 0.3% salt takes them down...
make sure to remove any plants you have though as they will have trouble surviving the raised salinity.
Also, were are you at with cycling? Is your tank fully cycled? Otherwise, the regime will need to include waterchanges to keep any ammonia/nitrites under control - especially as they'll need to be strong to come out of this unscathed