Sponge - Dead or Alive?

[euromomtx]

I ordered some livestock from a company and they substituted one of the sponges I had ordered for a different kind.
I had read that the red tree sponge was difficult to keep and that's the kind they send me.
My other sponges are looking pretty good but this one appears a bit 'fuzzy'.
So if these sponges easily die in captivity how will I know it's dead?
It's not like sponges move a lot...
Does fuzzy mean dead? What are some indications of it being dead (and potentially being a risk to my other critters)?

 

[Bongo Shrimp]

Well if you see grey areas around the colored areas, those grey areas are dead tissue. It would take a long time for it to completely die so it is not an immediate risk to your other critters, just watch it.

 

[TheH]

As bongo mentioned there will be obvious tissue necrosis and then subsequent algae growth.