I have had mine for about a year now.. He gets big and puffy if you mess with him or other things pick at him... but I have had fish that have lasted right along with him for that year. NOTE: I am not an expert, in fact, I consider myself a noob. However, I have kept mine in a 30 gal tank. I feed him PhytoPlex. (careful with this stuff though, too much of it causes your levels to jump fast.
I have never seen him eat, nor have I seen him do the opposite. He does open up his tentacles very frequently. He moves around when I change flow paths in the tank. I think they are smart enough to find their own sweet spot. I just recently got a 90 gallon tank and as an experiment I left the sea apple in my 30 gal tank. I put only one pump in the tank and the sea apple moved around the tank until he found that pump. Now he chills right next to the pump so that when he opens up he gets the full flow of it. from this I deduct that they like a lot of flow.
I was actually debating on moving him into my 90 with coral. Hence why I found this post.. I was seeing if anyone knew more then I did before I took the risk. Also as a side note.. I had him in with corals before. The corals were healthy and spawning during this time period.
Maybe I just got really lucky