The BRS video on aiptasia really put down the copperband butterfly fish. And I know this is anecdotal. But I got a copperband back in January / February. He was eating frozen food at the fish store. I made sure of that and appeared healthy. I temperature acclimated him then put him in my tank. OMG, he's an awesome personality, just an all around awesome fish that I thought I'd never have because it is expert care fish. He's been in my tank for 4 months now and my aiptasia went from tens of thousands to maybe a couple hundred or so. I found a couple smaller rocks that had huge chucnks of aiptasia that my copperband won't eat, so I pulled those rocks out. I'm finally having to search for them vs. seeing them in the thousands killing my corals. I watch the copperband and he's munching on aiptasia all day like it's potato chips. When I feed frozen food, he comes to the top and is almost ready to eat out of my hand.
The key is to make sure that it'seating good at the fish store before taking home. There's lots of information on copperbands online that I read before getting one. It needs to be actively hunting at the store, actively eating and searching for food. They don't really stop hunting. Their little beaks can only get so much food at a time so they have to eat in smaller chunks. Mine's beak is really powerful. He takes large chunks of frozen food and mashes them with his beak. Spits out what he can't eat and then catches it and mashes it more. When he attacks aiptasia. He watches them,circles them to see what the best angle to get it is. When it's ready, it's powerful tail fin lunges it forward to yank the aiptasia out before it cango back into hiding. He has given me hope that I will not be tearing my tank down and so far, he does not touch any corals at all. He may eat pods also, which is fine. I have a healthy supply.