this is how I make air powered filters for fry tanks; should work for you.
you need;
a soft drink bottle of the appropriate size for your tank
an air stone and preferably, but not essential, a UG uplift tube.
an air pump and air line
gravel and or filter floss or sponges
Cut the neck off the bottle to a height that is two or three inches shorter than your tank is tall. Put the uplift in, or airline with an air stone on the end if you don't have a uplift tube, into the bottom of the bottle. Fill with filter media; if you're using sponges, cut them up into small cubes; you'll probably need some stones or gravel to weight the whole thing down, but just gravel works perfectly well.
Put in the tank and switch on your air pump.
Do remember, that it won't be cycled, unless you use mature media, or your gravel is from a tank with a UG, so you still need to be tsting for ammonia and nitrite.
