Mini fish tank question?

i just bought a mini bow 2.5 aquarium kit about 3-4 months ago and Ive been noticing that all my fish have been dying for no reason. until i saw my new fish getting sucked in to the filter i have for it. it is a tetra micro filter. Ive put small rocks under it,but it is not working. can any one give me ideas what to do. i dont want to buy an expensive fish so it could just die.