they are weak.
if you have power head, power filter
those nudibrances will say good bye in no time
I have 4 of them in the past. I found 1 in the power filter (Emperor 400), 1 in the skimmer and no sign for the other 2. I'm guessing that my crabs have eat them.
I would not add any of them in my tank again. What a way to waste money.
Some of them are required algea and some required flatworms in their diet.
for the Lettuce Nudibranch(Lettuce Slug)
Herbivorous, green algea and photosynthetic (Julian Sprung)
Maybe someone else have better experience