Sorry for your loss.
Also a nudibranch has a zero chance of living in your tank.
You also seem to be adding more than one fish at a time.
Unless you have a very large tank you are heading to problems.
My I suggest that you get some books like Robert Fenner's Conscientious Aquarist and read up at
www.wetwebmedia.com
Also plan what you might be interested in and ask here for advice before you buy.