They are not considered reef safe because the will eat your inverts (Snails, shrimps, crabs) and they can knock over your rockwork if it not secure. They add a very large bioload. I have one in my FLOWR thats about 18 inches long and some where between a quater and half-dolar thick, I haven't had a problem with him knocking over rockwork or eating snails or crab (I actually have a 3-4inch spider decorator crab that lives in his caves add hangs out with him), I haven't got brave enough try shrimp. I also keep him very well fed. Just like every thing else in this hobby It is on a specimen to specimen basis, with they experence I have had with mine I might try it but thats just based off of my current SFE, Also a Snowflake will not out grow a 450 gal tank