Yeah in previous tanks I've had these guys and they totally took care of aiptasia. Unfortunately each one I did have eventually jumped (which incidentally is how I figured out they were doing the job because guess what came back afterwards?). This one I have now hasn't jumped but is otherwise kinda useless.
Not sure if it's wise to attempt a second one. I suppose I could try catching this one and moving him to the second tank, but that's kinda easier said than done.
Now that you mention the frozen food thing ... I remember the old ones were the same way (frozen and aiptasia all they ate). This one eats pellets. Go figure. Darn fish really need to get on the same page. It's like they don't even read the internet AT ALL.