Is this biofilm?

[grob]

I have a 65 gallon AIO and this is on both of my sponges in the middle chambers (not my side chambers with my media baskets and filter floss) Is it biofilm and what should I do? My tank is just over a year old.

 

[Subsea]

Yes, it’s most likely biofouling.

Remove sponges. Replace with reef rubble, if anything.