uh oh or not

[Robert1994]

this seems to be spreading

 

[Tahoe61]

How old is the tank?

 

[Flippers4pups]

this seems to be spreading

Can you be more specific in what you see?

 

[ScottR]

Hard to tell from the pic but looks like spirorbid worms. They’re harmless filter feeders but grow in numbers fast. More of an aesthetic thing.