white bacteria

Does anyone know what this weird white/clear stuff is? It’s almost like hair algae but it only grows on the underside of rocks. I’ve attached a gif and some photos (sorry about the in and out of focus and the six line he loves to be up in my business) We’ve have a 13.5 fluval and have been...

Hello everyone. I have attached 3 pictures of this white stringy stuff that appeared two days ago in my tank. I assume it is bacteria? Can anyone confirm or correct this? Thank you!