Don't let that get you down. Sometimes no matter what, the result is always the same. We can only try. If you still have the one that is alive, and if you're up to the challenge, try large daily water changes. Keep the tank pristine and feed whatever the fish eats now, bloodworms, even if it just nibbles. Its important to keep it eating because if its parasites, starvation makes it worse. If you can get your hands on Flubendazole, I'd most definately try that. The fact that the fish lasted so long is a sign it is not bacterial but parasitic/worm issue with which in the wild fish do just fine but not in captivity. A few months back I bought a sick clown loach. It took me 3 months, daily water changes and 4 meds to "fix" him and thankfully it finally worked. Now I have a little pig that is back to growing and eating greedily.