I am sorry to hear of your sudden problems. I guess I would recommend trying to QTing the fish seperately, 10gallons are only like $12 here. I also guess that it was your low Alk that caused the stress in the fish. I basically had the same problem occur and lost a couple of fish. Regarding catching the fish, I have hearding of people placing a piece a bait inside a jar for a few days, allowing the fish to get use to the jar and then spring the trap. Just an idea never tried.