Critters?

[AguaSalgada]

I just saw some very small critters in my sand. They were moving and now stopped.

Any idea if its good, bad, should i remove them?

 

[Tired]

There are dozens if not hundreds of species of critter that could be, and I may be drastically underestimating. Impossible to say for certain without, at minimum, a more specific description. That said, most small critters you'll see pop up in a reef tank are going to be harmless, and might well be useful detritivores and fish foods.