IME they (the one in the pic) will eat algae off the glass. they are a PITA
to keep out of overflows. for some reason they like the rushing water and
are attracted to the overflows. i always liked the Greek Goddess and other
then the overflows never had a problem with them. they are known to eat
anemones in order to 'move' the stinging cells of the anemone into their own
crown for a stinging protection for themselves.

kc