Sea Hare seems dead PLEASE HELP!

[Rogue951]

I've had 2 die on me in tank with nothing to show for it. (as in it hid somewhere and died) this is in a 20 gallon.
the only thing I did was turn the skimmer up full blast and let it run wetter to get anything out and also put in new changes of carbon/purigen.

tank didn't seem to notice.

If yours is non responsive even when you poke it, it's probably dead. Is it really firm when do poke? Do the breathing holes (one forward, one back of the rear hump) react if u touch the edges? if not then it's quite likely dead. I've found they shrink up and turn dark.