Thank you all for the great information! We went ahead and treated the tank with ethromycin (API). We did not have the info. on sterilizing plants, sbstrate etc. when we started the process. Sad to say, the second to last fish in the tank is now feeling poorly. He didn't eat tonight. I kinda think this is it. We'll just have to find another home for the last fish (after a q.t. of course) then I think we should just chuck everything but the tank itself. Will bleach do the trick with that? How long should we q.t. the last fish? Sad.