Complete Wipe Out.. Now: What fish to get?

[kambiz]

i have had a 55 gal for about 4 months now. lots of live rock.. before that, i was running a 25 gal. with just a couple of damsels and clowns in it..
7 weeks ago, i decided to add a beautiful butterfly to the tank. i watched him for a couple of days in the store to make sure he was ok..
i did not quarantine him before putting him in with the others. he was not eating for the first couple of days. then, i had to go away for 3 days, but just before i left, i noticed he has white ick on his body.
i returned after 3 days, and ALL the fish were dead.. my cleaner shrimp and crab had only left the skeleton of the butterfly!!
i ran the tank for another month to make sure whatever it was, had passed..
now here is my question:
what the heck happened to kill everything in 3 days?
i have since got only a large sri lankan clown and a small 3 stripe damsel. and they seem to be well. but i want to get a larger fish something hardy and colourful. (possibly a tang).. but everyone says tangs are prone to ick. so i am questioning my choice.. i do not want the fish to get sick again.. (it is hard to loose fish (sure you guys know) what can i add to the tank?
ps. i continuously attend to my water, and it always has been good..

 

[kambiz]

ok.. so what hardy and colourful fish do you recommend? assuming i am planning to run a quarantine first? have always liked triggers, but i don't want to take a chance with my cleaner shrimp. i have had HER for about a year now, and she is HUGE.. she actually laid a lot of eggs once, but all the others ate her eggs. it was cool to watch.. she had all these eggs under her belly, and would regulatly "move, reorganize and shake" them..