sea slug acting strange

[xnikki118x]

I just watched my sea slug float all around my tank for like 5 minutes before finally attaching himself to the filter intake. I just want to know if this is normal? I'm not sure if it's a sign of stress or illness or anythiung like that...he never floated around like that before.
Water parameters:
ammonia = 0
nitrite = 0
nitrate = 0-5
pH = 8.2/8.3
alkalinity = ~10
calcium = 520
Tank inhabitants:
false percula
blue velvet damsel
yellow tang (small!)
coral beauty angel
long-spined urchin
cleaner shrimp
lots of crabs and turbos
tree leather
some assorted mushrooms
2 or 3 feather dusters
Here's the kind of slug it is:

 

[schneidts]

Hi,
I hate to be the bringer of bad news, but your slug isn't going to live very long, I'm afraid. I'm not sure of it's common name, but it's scientific name is Chromodoris Elisabethina. They feed only on a species of sponge, and they will starve to death without it. How long have you had them and where did you get them? Here is a pic of them feeding in the wild.

 

[effloresce]

sounds like tis already dead, they dont freely attach to filters....

 

[xnikki118x]

Well, he's grazing along the live rock again, so I know he's still alive at least.
I've had him for about a month, and I got him from the pet store I work at.
He only eats a certain species of sponge? Is there any way I can get that sponge?
If I can't, how do I know when it's dead?

 

[schneidts]

I'm sorry to say that you can't get that species of sponge. Unfortunately, the slug is doomed. The one positive thing that you can do, is advocate to the owner of the store that nudibranches should not be collected, as 99% of them die. There are a couple of species that can be kept, such as Elysia crispata and Berghia verrucicornis, and even possibly Chelidonura varians, all of which are very delicate and require their specific diet to be kept in captivity.