Learned through brother's mistakes. He was always too impatient to quarantine anything. But, he eventually lost all of the fish in his display tank to ich except for the yellow tang. Then, he finally listened to me and set up a quarantine/hospital tank. Left the display tank void of fish for a month to make sure the ich was all gone before putting the fish back in. I've always quarantined my fish. Would never take the chance and potentially muck up the display tank.