Mysterious Creature ID

[Lillypad101]

Hi everyone! I saw something strange in my saltwater tank today. The lights have been off for about 2 days now. They are off because of an algae problem. These creatures look like tiny shrimp with a stripe going down their bodies. These things are small. Not that small for a copepod or the like though. About 3 mm.
Here are tank details:

55 gallons
Canister filter
Heater (not sure wattage)
Temperature is 78
50 pounds of rock
60 pounds of live sand
Ammonia: 0
Nitrite: 0
Nitrate: 20

Stocking:

Mandarin fish- have lots of copepods/cultured and bred in the tank/extra dose every other month. He also eats frozen foods.
Linear blenny
Orange skunk clown
Hector goby
Sun coral
Hammer coral
X2 urchins

This tank has been set up for a little over a year.

Any advice appreciated!
Will get pics tomorrow!

 

[Colin_T]

need better pictures but I'm going with Gammarids, which are harmless and nothing to worry about.

 

[Lillypad101]

thank you! I looked them up and that’s exactly what they look like! Sorry for the very blurry picture… how did they get into my tank?

 

[Colin_T]

They would have come in with some plants. They eat anything dead and organic (fish food, dead plant, dead fish). They are interesting and will breed in an aquarium. The bigger fish will try to eat them but the smaller fish will ignore them.