Mysterious holes in sand

[leafyseadragon]

It seems every week I see something new in my "empty" tank. I was looking at the sand right next to the aquarium glass, and I can see some small holes just below the surface of the sand.

What made these?

 

[brndfrb]

I would say the holes are from pods or something like that. It could also be from the sand just settling. Not reall sure someone else might want to chime in here.

 

[reefrunner69]

There is the possibility that your seeing worm tracks or even some nitrogen gas building up in your sand bed (good thing).