We refer to several tiny crustaceans in the hobby as 'pods'. They are copepods,amphipods, and isopods. What you have sounds like a type of isopod. Copepods are very tiny..like specs, and flit about in the water column . They also congregate together in groups...sort of like gnats do. Amphipods are shaped sort of like a 'C' and scurry along the bottom and in the rocks. They also do this spin thing..where they flip over. Isopods{the most common ones in the hobby} crawl around up the glass,and have legs that make them resemble a bug. There are also live mysis shrimp that can be in your tank..much larger than copepods..they seem to swim aimlessly back and forth. If you shine a light on mysis at night, their eyes glow.