Maroon Clowns/BTA

[FearsomeB]

I've had two maroon clowns for approximately 4 weeks and they are getting along fine. I recently got them a BTA. The BTA was smaller than the female maroon, which was a mistake on my part. She was so eager to host in it that she literally started beating it and pushing it around. If that were the only issue I'd chalk it up to experience and buy them a larger BTA next time. However, she also started chomping all off its tentacles. I saw her taking them into her mouth yesterday and I saw other people referencing similar behavior online without ill effect so I wasn't that worried. Today when I got home from work, it appeared that someone ran a lawnmower across the BTA. The two clowns are still rubbing aggressively against it, even though all of its tentacles are gone. Is this normal/how can I prevent something similar happening if I get them a suitably large (and more expensive) BTA?