Tangs nipping acans

I'm suspecting my grazers are nipping my acans causing them to stay closed up.

Nothing changed equipment wise and all levels are still good I read horror stories about people losing acans to their tangs. I Have some pretty expensive acans and would hate to lose them. Im giving them nori everyday and looking for any tips or advice to try and get them to leave my corals alone. Thanks guys hope you can help