Even species that leave the Green Mandarin alone can cause problems by
gulping down all the food before the Mandarin gets a chance to catch any. They are known to be quite intolerant of their own species when kept in small aquariums.

The Green Mandarin is considered reef safe, but it may nibble at small coral
polyps.

The aquarium where you keep your Green Mandarin should contain plenty of
suitable hiding spots, such as caves and crevices. A Green Mandarin that is kept
in a barren aquarium can become very stressed and shy. If you have a Mandarin
that stays hidden all the time, try including even more hiding spots in the set up.

If you want to keep Green Mandarin, you should ideally wait until you have a
well established aquarium with plenty of live rock  because this will make
it possible for the Green Mandarin to eat naturally occurring tiny animals just
like it would do in the wild.

Generally speaking, the aquarium should have been active for at least six months
before you introduce any mandarins.

Ideally avoid using  ultraviolet filters in the aquarium when keeping
Mandarin, because such filters can kill organisms necessary for a well
functioning ecosystem that provides the mandarin fish suitable food.