I forgot to say about the quarantine period, shame on me !!
But like everybody else says, it's very important. In the beginning of our garterhobby we've made that mistake once. The newones seems healthy in the beginning but within a month all the 6 died and a few of our others as well
(btw we bought them from the wrong kind of people, we know that now)That was a hard lesson for us, so now we have a few quarantine tanks in a sepparate room.