Red tip sea goddess = Glossodoris sedna, family Chromodorididae. All chromodorids are specialized sponge feeders so without the right type of sponge in your tank it will die. Unfortunately, no one knows exactly which sponges it eats and even if it was know, it's unlikely they'd show up at a LFS. Sponge eaters tend to concentrate the defensive chemicals made by sponges in their own bodies. Some nudibranchs - notably the phyllidiids - are so toxic they can nuke a tank when they die or release the chemicals.