Return the copperband to the LFS that you bought it from before it gets bullied to death.
Sell all the tangs you have in your tank and replace them with a few fish suitable for a small tank like yours. I plan to upgrade my tank in 6 months does not cut it for me, sorry.
Buy a peppermint shrimp and very slowly acclimate it and it should remove the aiptasia.
+1
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One more fish should be ok?, right!!! - Laurie