Finger leather needs help!!!

[pat]

Hi everyone
I have a 66gallon reef tank with only a few coral.
1-toadstoll leather
1-colt coral
1-fox coral
Assorted mushrooms
Yellow polyps
2 different types of green stars
1-condy
1-bubble tip
1-feather duster
Fish;flame angel,yellow tang,maroon clown,1blue damsel,2yellow tail damsel,bi-color blennie,lawnmower blennie,scooter blennie and 2 green chromis.
Lighting is;1-175wM.H(not10k),4-20wactinic(marine glo)and 2-55w power compact.
Filtration:sump wet dry with sera syporax bio-balls,sea clone skimmer,aqua-clear200 hang on in tank.

Well here is my probleme! everything in my tank look very happy exept my finger leather coral.
When i fist introduce it in the tank it was happy for about 1 week.
It started to shrink and shrink,now it seams to be coverd with some brown slime!?!
Is it dying???
What should i do???
Tank you
Pat