Hie Darkhorse,
I don't know why everybody is going bannanas about amonia and nitrates.

Bubbles for oxygen are great and so are charcoal filters and other filters. I personally think that the chemicals added may cause the little healthy fish more harm than good. I have a normal filter at home and over the aquarium I have a sieve with a hankerchief (rinsed to contain no washing detergent, Very Important!) and a small plastic basket containing carcoal inside the sieve. Then I attach the tube to the filter outlet and put the other end of the tube over the charcoal filter and stabilise the tube with two pegs attached to the sieve. This is very economical and effective for reducing water impurities.
Cheers
Hoover the Goldfish