Sea Hare seems dead PLEASE HELP!

[Frenchie2]

I got a Sea Hare last week to get rid of HA and it has done most of the places that needed to be "mowed" except for one area. Tonight I'm looking in the tank (90g) and I see the sea hare a bit shrunk and kinda of "floating" near a coral (devil's hand - I saw the sea hare last night on this coral seeming like sucking on it...). I poked it here and there and it is definitely not reacting to anything... I'm worried about the tank as I read a few "horror" stories about sea hare dying in a tank that can completely wipe your tank... I took it out and put in a container and it still not doing anything... What should I do?? Should I run any carbon in the sump? PLEASE ADVISE ANYONE ASAP!!!!