Random Sand Vertical Formation?

[Zaxh]

Any idea what this is? I just looked at the back of my tank (Working on my GHA lol). It's so weird... Are my fish getting smart?

 

[ISpeakForTheSeas]

Probably a worm's tube.

 

[Zaxh]

Probably a worm's tube.

Friend or Foe?

 

[ISpeakForTheSeas]

Friend or Foe?

Most likely harmless, though we'd need to see the worm/its feeding methods to know for sure, and if you get enough of these little tube structures it can be annoying/slightly problematic.