they look like amphipods. Can you tell is the tail on them curly like (are they curly when they aren't moving) ?
Check the -> images <- and compare please, as I can't see more from the photos.
+1 on amphipods. They’re good. Sometimes really big ones drum up debate on whether or now they’re doing something they shouldn’t. Ie. Eating copepods, picking at coral, irritating coral etc.
They're probably in every reef tank so you’re on track.