To me quarantine is isolation from any other animal. Not just tanks, or rack but in a totally separate room. If you are a week or two into the 30 day treatment and you bring in another new animal that is basically making you start the 30 day treatment all over again. Each new animal is a potential host.

I've had several times where a new animal was brought in with no signs of mites but after two weeks in quarantine then they start appear but only sporadically. If I bring in two animals in a close time frame then they are both kept separate from each other (while in quarantine) and from the rest of my snakes. Even if two snakes come from the same breeder they are still quarantined separate. You never know if someone may have handled the one of the snakes at a show and transferred mites. It's a whole lot easier to treat a single animal that is still in quarantine than it is to treat a whole room full of snakes.