What eats mdntipora eating nudibranch?

[Gregorioscapes]

I have a 20 gallon nano aio and just recently my Monti caps went from healthy to bleached in a few days. I discovered I had Monti eating nudibranchs which probably came in as eggs. Will anything eat these? I've been keeping my nano reef empty in the way of fish but I would like to add something to control the population.

 

[Mike konesky]

Sixline would be my pick.