amphipods i think???

[trouble]

Went at my tank with a flash light one night to see if i had any bristle worms(I have at least 5-6 of them that i have seen) and noticed these little brown buggers that are extremely fast and range from a couple mm to a few mm in length. research has taught me that the bristle worms are no big deal but as far as i can tell these other little guys are amphipods other than that have not been able to determine if they are bad/good, or how to control their numbers (or even if controlling their numbers is necessary),since they seem to be quite plentiful, thats actually an understatement as their seems to be hundreds of the little things. can some body shed some light on the subject for me