Unfortunately, they had to die at some point. Had they not died of diseases, they would have died of old age. (Unfortunately the nod has a smile)
If it's any consolation, you tried. If you've had them for years, you didn't make any mistakes.
The best thing to do now is just move the fish and tear down the tank and rebuild. At least you'll be able to start over, if you want (which may not be much consolation, I'm sorry.)
Sorry to hear about your fish You mentioned in your first post that you've changed the water conditioner. I'm curious to hear what you were using before and what you're using now...
Greathat, I'll join you and cry with you. In the last 2 days I have lost 3 of my fishies (they got ick) I'm treating the rest but they don't look happy.
But at least we tried to help help and they know that we love them.