A simple setup for a famously tough fish
Zebra danios forgive beginner mistakes that would finish more delicate species, which makes their quarantine refreshingly undemanding. A small tank, a cycled sponge filter, a heater set modestly since danios are content in the cooler half of the tropical range, and a lid fitted like you mean it: danios are committed jumpers, and more are lost to a finger-wide gap at the back of the hood than to any disease. Keep the new fish together as the school you bought, because a danio alone is a stressed danio, and add a plant or two, real or silk, so the group has somewhere to swirl around. That is genuinely all the infrastructure this fish asks for.
The danio-specific things to watch
Hardiness hides two particular problems worth screening for. The first is the thin fish: some new danios arrive with a hollow, pinched body and fail to gain weight despite eating, a wasting pattern that can spread slowly through a school and is far easier to spot and isolate in quarantine than in a busy display. Weigh them with your eyes daily: backs should look filled out, not knife-edged, and bellies gently rounded after feeding. The second is the usual run of white spots and fin trouble, which on a fast fish is easiest to check at feeding time when the school slows down at the surface. Also look for any individual with a bent spine that was not bent at the shop; it is a reason to keep that fish out of a breeding group, though it may live a normal pet life.
Feed, watch, and read their energy
Healthy danios announce themselves within hours: the school races the length of the tank, squabbles cheerfully over flake, and investigates everything, including your fingers. Feed a small portion twice a day and confirm that every fish in the group eats with that trademark enthusiasm, because in a school this boisterous, the one hanging back at the rear is displaying the only quiet symptom you may get. Test the quarantine water every few days, since even hardy fish deserve water that is not sliding, and change a portion weekly. A few weeks of this, with every fish plump, spotless and frantic at feeding time, is a complete quarantine for this species.
When the school joins the main tank
Acclimate the group to the main tank's water gradually and release them together, ideally with the lights low, then stand back: a settled danio school will be exploring the full length of the tank within the hour. Make sure the main tank's lid discipline matches the quarantine's, and give them the swimming length they crave rather than a tall, narrow water column. Before the move, add the short quarantine summary to the school's KinsLe Pet Passport, arrival date, condition on arrival, how they fed, and the day they were released, so that if the school ever thins or fades months later you have a dated record of exactly how they started with you.