I purchased a green lettuce nudibranch about a month ago. He eats some algae, funny thing though. Hos favorite spot is on the glass where there is only a slight film of algae. I have to always clean around him/her/it? I was told that they eat algae as they need the chlorophyll (?) to help them with photosynthesis. They get energy from the light like plants do.
Iv'e made several misinformed purchases. One was a "reef friendly" Sand Perch he grew from one inch to six in about 3 months. Found out he likes feather duster feathers and peppermint shrimp. caught him with a piece of cocktail shrimp in a small jug with my ice fishing pole (barbed flattened) now he is for sale again at the lfs
The other was a fish sold to me a Scooter Blenny but as it turns out it is a much more expensive Mothers Sailfin Dragonet. It has the most spectacular dorsal fin.