I'll be totally honest and say I've never quarantined a fish in my life
yes, I know I know.......
I observe all fish extremely closely for a couple of weeks after adding a new purchase. (Touch Wood) the worst I've encounted (actually the only thing ever) was a dash of ICH which was nipped in the bud very quickly with no loss of fish.
Same hereI'll be totally honest and say I've never quarantined a fish in my life
will have them get a non sick looking fish if I really wanted the fish that day
id rather spend that money on fish that on another tank and all the equipment needed to run it.
I try not to buy any fish that looks sick.
I've had new fish die of columnaris or something of the sort, but have never had it spread.