i defenatly wouldnt add any human anti bacteria (not saying it wont work but its a big risk you could do more harm than good)
i wouldnt take the fish straight out and trim the fin its a lot of stress
i personly would sedate the fish with 4 drops of clover oil for 1g of water do it in a jug so you would need 2 1g containers one with 4 drops of clover oil in the other with plain tank water add the fish to the clover tank wait intill the fish is almost mosion less check with a net then pull the fish allmost out of the water keeping its gills wet and trim the fin then add the fish to the 1g tank with tank water move the fish back and forth to get water through its gills and it should regain conconess give it a 30 min brack to recover then you can add it back to the display aquarium
(warning do not keep the fish in the clover oil tank for more than 3-5 mins any more can kill the fish so get the job done quick this is only an idea its commonly done for puffer fish)
I completely agree with you I took the risk because he was a feeder goldfish. how ever I was suggesting it as a last resort. if hes tried everything and nothing works and thes fish is gonna die might as well give it a try
heres a vid link of it being done to a puffer but you would trim its fin not its teeth
http://www.youtube.com/watch?v=qJzJtH2e2bg