Alien white algae ?

[SahnCH]

Hey everyone !

My tank is around 14 months old now, I'm having weird white algae on rocks, they easily goes away when brushed but I have no idea what they are.
Also never seen any of them in other's video or picture, would you know what these are ?
https://www.youtube.com/shorts/XKG-1pUQHRU

thanks for your tips!

 

[Court_Appointed_Hypeman]

I have those, I assumed they were a type of sponge because they blow off when I go a couple days without dosing silicates.
Watching to see what others say.

 

[ISpeakForTheSeas]

I agree, they look like sponges to me (harmless filter feeders).

 

[MichaelReefer]

Sponges.