put some more live rock in my nano today and this appeared on the front of the tank, any ideas? sorry about crappy pic but hard to get a better one and it's disappeared now!
Some are bad. Some are not. The thing about nudibranchs is that they only eat one thing in their diet. Like I said, some eat zoanthids and are bad if you have any. Some are just hitchhikers that end up dying from starvation because the tank does not have their natural food source. I am not sure what type you have. Maybe someone else can help on the specific ID.