What is this growing in my tank

[reeferk2]

Hey wondering if I should be worried about this dark brown stringy stuff in 6 month old tank, I blow it off and it comes back almost immediately mostly on sand alittle bit on rock scape, will it eventually go away or don’t need to deal with it

 

[TARHEEL78]

You're going to need to post white light pictures to get any ID.

 

[reeferk2]

Are these better

 

[Dodge Ram]

Cyano. That is what comes with every tank and fish. Nutrients and light feed it.
Got a bit of that in a couple tanks.