I had a VERY hardy cichlid once. He was an adult and I was keeping him in a small tank (that's what he was given to me in and I had no money of my own at the time). I have no clue what species he was, and I don't have any pics and just barely remember what he looks like, so I guess I will never know what he was.
Anyway, I named him Thrash because he was mean as hell. At the time I had no idea there was chlorine in tap water, so I never used any chemicals to make the water safe. I had him for about a year, so of course I did several water changes and he survived a year with just straight tap water. One day I guess all the chlorine finally caught up with him, and he died.
That's the worst experience I have ever had with fish.