White root like growth on back glass

[gfrowen]

Hi,

currently running a fallow tank after an ich outbreak. About 2 months fallow now so almost there.
However, I’ve noticed this structure growing on the back gLass and also around one of my inlets to the tank.

any one have any idea what it could be???

many thanks in advance

 

[fishface NJ]

Look like a sponge

 

[gfrowen]

Look like a sponge

Thanks for replying so fast.

it’s really flat. I can only describe it as looking like the roots of a plant when you pull it out of the pot.
Just seemed to appear out of nowhere really.

does it need to be removed or is it harmless???