Poor guy, I would take him out of that container and put him in something else immediately. If you have a never-been-washed or new piece of gladware or a plastic rubbermaid/sterilite storage bin, you can keep him in that temporarily with a little extra dechlorinator than usual. If you kept his cup and you have nothing else, put him in that for now with 100% new water. He may bounce back, and even if the fish does end up dying, it is inhumane to let him die a painful death immersed in chlorine--at least let him pass in clean dechlorinated water. If he is still eating and swimming around, he may live. If he is simply at the bottom gasping and can't be motivated by food, will likely die, and it is probably a good idea to euthanize him.
The two most humane euthanasia methods are blunt force trauma (putting the fish in a folded wet paper towel, and crush him with a blunt object--sounds brutal, but is the fastest and most painless), and immersion in clove oil solution. Clove oil can be found in the dental section of a pharmacy or GNC--sometimes called Eugenol, for tooth pain. This is an anesthetic that makes the fish unconscious, and then the overdosage eventually puts the fish to sleep. The problem with this method is that sometimes fish can revive from it, so start with a few drops, and then add more and wait until you are sure he is completely dead. Flushing, freezing, suffocation and decapitation are all inhumane and should not be considered.
As for the tank, how big is it? If it is smaller than two gallons, personally, I would take this opportunity to upgrade. If it is larger than that, you should completely wash everything out again with hot water, and then use an overdose of dechlorinator to help detoxify the chlorine. Bleach is basically concentrated chlorine, so your dechlorinator should help you remove some of it. You should let the tank and everything you washed with bleach completely dry out in the sun. This will evaporate what is left of the bleach. It may be easier to spread the gravel out on a big black trashbag and use a hair dryer on it--I've done it before, lol.
Last edited by Adastra; 07-15-2010 at 04:38 PM.