I'm guessing this is Cyanobacteria

I have a rock in the front of my cube that likes to trap crap behind it. I pulled it out and started to vacumn out the waste and noticed these brown strings similar to grass growing below the sand. I stirred the sand in this location and sucked out the cloud as it stirred up.

My question is, what is that grass stuff?

 

Do you have a photo?

 

Doesn't really sound like cyano, but there are a number of strains of cyano. I don't think it is the typical purple slime. A pic would be great though.

 

Finally found a spot where I could take a pic without disturbing much. Any ideas what this is?

 

Tubeworms. 99.9% of the time they are harmless......they just aren't pretty. Every once in a rare while, one gets so many of them that they can almost solidify a sandbed. I pick them out with tweezers.....you have to get down as far as possible before pinching. Otherwise, they'll just retreat inside their tubes below sand level and all you are removing is their paper-like tube which they'll just regrow.

 

tube or flat worm !!!!i think it's flat

 

I just stirred up the sand and they dissolved into a brown cloud in the water. Im hoping that they just stay away as long as I keep the sand stirred from time to time.

 

tube worm! It never did any harm to any of my aquariums, but I HATE the way they look.