She bought the fish? Does that make you a kept man?
Filter:
A plastic shoe box with a fountain pump mounted inside. Cut a hole in the top for the fountain head pipe, and 1/2in holes around the sides and top for water entry to filter (bottom too if you want. Put quilt batting in the box for filter material (cheap) (put a piece of screen material around the pump inlet) . And use a bell shaped fountain head (it's pretty, gives alot of surface area without height, & alot of splash to the water). You can paint the box black or glue gravel all over it so you can't see it.