Yes, what you see is real and yes it is colonizing in your sand and live rock..
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Amphipod
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And their much smaller cousins -- The
Copepod
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Don't worry, even though they look like something straight out of Alien vs Predator, these microscopic shrimp-like crustaceans are extremely important to the foundation of your SW setup. Amphipods and Copepods range in size from 1mm to 140mm (5.5"!) Not only do they scavenge and clean the rock and sand, but they also can provide an abundance of meals for Wrasses, Dragonets/Blennys, Hawkfish/Hogfish, Tangs, Angels and even Clowns etc. They are prodominately nocturnal but may also be seen in the day (the dumb ones), just before being snatched up quickly by a passing fish.. Now that you know, you will be noticing a lot more of them.. Anyways, just thought I would humble you with a couple interesting tidbits of Reef Biology.. Pictures of your tank look great too thank you for sharing!