once again dude,
please get a huge tank first, all your filtration, show us some pics then maybe someone will help you find what your looking for, but until then i doubt anyone is goign to answer you since you only have a 20 gallon tank.
im not tryin to be mean, we will all be glad to help you out, but ask some better questions first, such as, how big of a tank do i need ot hous ea small shark? what kind of filtration etc.
also since i see your a student, i will warn you its gunna cost you about 5 grand to get get a good shark setup started and running. its alot while still in school!!