small critters swimming and crawling

[theponds]

I have a bunch of small (3mm) critters running around in my tank. They are opaque with a brighter head. They appear to have antenna and about 8 legs. These critters are swimming and crwaling on my plants (which have been in the tank for several months) and crawling into my substrate (crushed coral). Any ideas what these critters are? Should I be worried?
Thanks in advance

 

[hunterdaddy]

Safe bet would be amphipods. They are safe and actually a good sign of a healthy system.