I have had mine now for 18 months. It eats anything and everything in the way of fish food, including pellets and flakes. It gets along well with all inhabitants of my tank. But as JT mentioned above, it developed a taste for zoas after I had it for about 4 months, and it cleared out all my zoas, and tried very hard to eat my palys but couldn't quite manage it. Nontheless, the Palys were damaged and remained closed, til I relocated them to another tank. I found, especially in the beginning, that the Idol doesn't eat a lot, but really seems to need to eat often.
I should also say that in the last couple of months, the idol has not looked as good as before. It has lost most of its streamer, which they do anyway, but it hasn't grown back like it normally does. The change in health seems to coincide with when I raised the mag to combat byropsis. So, its poorer condition may be due to the higher mag, or the lack of byropsis (the Idol used to eat it), or none of the above. Blackish markings appeared on the dorsal fins when this happened - I don't think it is a disease, but rather an indication of bad health. However, it is still acting the same as always, and still eating like a pig, and lately has started to look a little better. So, hopefully it will regain its health. It has been a really great fish to have, and I hope I can keep it a lot longer, because it is really my favorite.
By the way, I have it in a 240 gallon mixed reef tank. Other fishes are 2 Blue Devils, Rabbitfish, Asfur Angel, Yellow Coris Wrasse, Purple Tang, Achilles Tang, Mandarin, Scooter Blennie and a Majestic Angel.
Here is a little film of it:
Some pics:
Night time coloration: