How is the mushroom doing? When you say "fine", what are the parameters?
What kind of flow is pointing at it? Generally speaking with polyp type stuff they wont open if there's too much flow or if there's a fish messing with them - I had to move a few polythoas around a little bit until I found a place they were really happy in - away from any direct flow, and kinda separated from too much indirect as well. Also, depending on your lighting it may be too much/not enough. While you don't want to move stuff around immediately, I'd say that after 5 days or so it might be worth trying a different location or modifying water flow etc...
firefish, ocellaris clown fish
caulastrea, green star polyps, palythoa, zoas