Well heres the deal with carpets, Thier tenticles are SUPER STICKY. I mean STICKY. PLUS they pack a nasty sting. One sting wont necesarily kill a medium sized fish like a tang,but it may stunn it long enough to get stuck on those super sticky tenticles then its all over. If you do get one place it near the center of your tank on the substrate and hope it stays put! LOL!
Fish usualy get hit at night when they "settle" to close to it and the current sways them to close.
I just sold a blue S. Haddoni carpet that I'd kept for about 4-5 years. In the time I've had it, I lost two fish to it.
A mandarin and a possum wrasse.
While I kept the anemone, there was also a red flame hawk, a purple tang and a blue damsel in with it. These fish lived peacefully with the carpet in my 120 gallon reeftank.
One observation, and one that another carpet anemone owner has also noted -
If possible, place the carpet close to a vertical rock wall, so that the oral disk is not lying flat on the sand/substrate. If the carpet is allowed to lay flat, I think (can't substantiate) that fish can't see the predator to well and end up getting too close. I have a pic of the orientation of my carpet posted over on the BRS website. I'll pm you a link so you can see what I mean.