Yes, they have found a great place with which to live as it is dark and their is basically nothing to feed upon them, nutrients, water flow and ideal conditions exist there for them to survive and thrive.
All are great additions to your tank and I would leave them be...if cleaning the sponge/filter media, rinse it under salt water from your tank to ensure that the bacteria, other microscopic and beneficial lifeforms survive.
Blob is possibly a type of sponge...but will have to research it further, as I also have those living in my filters! _________ 125gal.w/Mag9.5 return(dual megaflow)>Mag7 pump Aqua Cev180skimmer.Wave2k Hamilton Reefstar(2)250watthqi(mh)pend.a Yellow, Naso Tang Red Lip Blenny Percula Clown Demoiselles Niger Trigger F. Wrasses Ceriantharia Orn.Shrimp and Stars Hermits Queen Conch asst. snails> Stars Zoos shrooms Montipora Brains Gorgonians Favia Turbinaria(large+small polyp) Acropora Xenia Tridacna (CroceaMaximaSquamosa) Leathers <35+75gal.reef tank as well> 
"IF THE PHONE DOESN'T RING...IT'S ME"  jb  | 
A breeding ground?? 
