Bought this frag and noticed this algae. It is not bubble algae. Shiny, green and forms in layers. I used a blade to remove and used 12% peroxide to carefully scrub the plug. Yet I found some on another frag this morning and one even in the rock.
Depends on the snail but the blenny should eat it. It is one of the fastest growing macro algaes since it is only 2 cells thick. You can always remove it if you'd like, it just becomes more of a mess later if you remove it when it grows since it is so brittle.