Help needed urgently

[rogesue]

Hi I need som help!!!! I need to urgently remove a pest fish from my tank. I recently purchased some Zoa's, then this fish consumed my beautiful Zoa's. The fish is a dark Blue Damsel, it is a lovely looking fish and fine with everything else, just not Zoa's. To anybody who is clever and confident of catching this thing, it's yours! Or just some advise would be greatly appreciated. I have tried the obvious methods with no success. Thanks!