Tree Sponges come in various colors. When buying a sponge like this from your LFS, you want to have it bagged while fully submerged. Bring it home and release it in your tank submerged so that it never comes in contact with air whatsoever. Sponges are filter-feeders and need moderate current. They don't rely on lighting; they need nutrients to survive. Large Angel fish feed on sponges, but these will be safe around dwarf angels.