Im going to agree with Lion. I kept a large naso with my shark with no issues but I know angels are always trouble. I got rid of the tang due to the fact that it went after my rays. He never bothered the sharks, but Im sure some will. If you do a tang, watch it closely- especially with the lights off. Wrasses are more prone to pick on rays than anything. The rays are covered in a high-protien mucus that they love to snack on. Sound yummy? I myself have kept tusks with rays though and never had a problem. HTH,
-Gas