how old is the tank? I had a huge amount of the sponges grow in the first few months I think it is from high nutrients. When everything stabilized they went away.
Yea things are still stabilizing I would think lots of life will bloom and then fall back. I had a billion fan worms, Bispira in the sand at one time, then a load of Spirorbids, then sponges all died back to normal non plague like proportions in time. Was fun to watch