I have a sebae anemone in 30 gallon, with two maroons. The maroons are just in there for quarantine, but the sebae is about 10 to 12 inches wide, she is huge. She is very happy, and has grown a lot in there. she is very attatched to where she is,but im scared that one day she will detatch and get sucked up into the powerhead that is in there to create water flow for her. your water quality has to be very good, but it is possible. I wouldnt advise it because mine is taking up more than 1/3 of the tank right now. I think that a small BTA is fine, as long as your water stays good.