Unfortunately their are hundreds of different types of nudibranches and each and everyone has a unique diet. What this means is it is VERY hard to care for one unless you have one that eats the kind of algae that is growing in your tank. I have a sea hare which is the same family and it appears to munch on the algae growing on my LR. I have no idea what exacly the type he is.
He is also ugly as it gets.
Most are don't live very long because they will only eat just one thing and only that thing. Could be caulerpa, hair algae, red sponges, aiptasias, anything, but that is all they will eat.