What is this?

[casper3t]

i got these little white stuff and they're a lot of them but then i started seeing more of these little guys... and they wont' go away

 

[Fluff]

Probably amphipods.
Check here for a pic to compare. http://www.reefs.org/hhfaq/pages/main_pages/faq_sand.htm

 

[casper3t]

my tank is infested with these guys, what fish or inverts can i buy to eat them?

 

[Fluff]

Why would you want to be rid of them? They are great for your tank. Also, their numbers will rise and fall depending on the food source.
But, if you have room for another fish, gobies eat them.