I saw a 5 gal tank at Wal Mart (by Aqua Tech) which uses a bio wheel filter and have a few questions. (1) Can someone please tell me how this filter works different than the regular cartridge filters? (2) Is a five gal tank too heavy to sit on the desk top of a 6 x 8 cube? (3) What kind of fish is recommended for this tank size? Thanks for your help.