"Sponge" Pest or no?

[CnjClarke]

My husband says this is a type of harmless "sponge"...I am not so sure. Our 20 gal tank is about 8 months old, we know we have some aptasia (trying to deal with it...sigh). These soft, small branch like things seem to be multiplying rapidly on the rocks. Any advice gladly taken as to 1) what they are and, if a pest, 2) the best way to deal with them! Sorry I am not the best videographer :-0

 

[Timfish]

Cryptic sponges are hugely important to reef ecosystems. So long as it's not one of the handful of species that encrust over corals I'd leave it. Cryptic sponges remove labile DOC (aka carbon dosing) that causes issues with corals 1000X faster than bacterioplankton and provide DIC (disolved inorganic carbon, HCO3 {alk}) back to the system for corals to use. If it really bothers you you can siphon it out easily.

 

[CnjClarke]

Thank you Tim!!