Identify the critter

[TrishW]

These are in the isolation tank that is inline before my sump. There are always a few visible but there are many more when it is lights out. They range in size from 3/16" to 1/2".

What are they?

 

[Lionfish Lair]

Amphipod.

 

[tyler1503]

+1 amphipods.
They're good guys to have. They're free fish food!