Can someone help me identify this?

[cruizbran]

While I was cleaning my tank I found this little guy. Is he a pest? I am thinking nudibranch, but someone told me that if it’s not white it may be eating my corals.
I’m adding photos from what it looked like inside and outside the tank.

 

[redfishbluefish]

Looks like a zoa eating nudi! Some confuse it with a berghia nudibranch which tend to be whiter, larger and have more "legs." The other sign is if you have zoa's they tend to close because of the nudi's eating them.

 

[Ultimate Corals]

It's a nudi that's eating something red. Possibly zoas. I would look into getting either a yellow coris wrasse or a melenarus wrasse in the tank. They will continually eat them so the numbers ween out.