Unknown on tank

[Taiko713]

A friend of mine just sent me this pic of something he found on the glass of his tank. Does anyone have an idea of what it may be?

Thanks

 

[F i s h y]

No idea. Haven't seen something like that before.

 

[Crabs McJones]

Red bubble algae

 

[Taiko713]

Really? It's not in my tank so this is the only image my friend sent me. Never seen anything like this