Overcrowded tank

[JamisonBWolsh]

You never mentioned at what your nitrates are??? Do you have a nitrate test kit?

A Fluidized bed filter is this:

a powerhead in a tank that blows the water to a slim (usually see through canistor that holds sand. The water goes through this sand and out the fluidized filter bed. Here is the KEY: The good bacteria lives on each individual grain of sand and you have the MOST good bacteria you can get! You will NEVER get any ammonia or nitrite problems

Your right on the inch per gallon rule. Its a tool to start with. Then you calculate how well you change the water, what type of fish.

 

[JSchmidt]

Unless you're having problems with ammonia/nitrites, you probably don't additional biofiltration. As long as your dad doesn't add any specimens, your bioload should increase slowly enough (as the fish grow) that the biofilter can keep up. A fluidized bed filter, although cool, probably won't give you the most bang for your filter buck.

I'd advise that you get another mechanical filter, one that is so easy to clean that you can do so several times a week. (Frequent cleaning of mech filtration in an overstocked tank is a must, IME.) A HOT Magnum with a sponge prefilter or an Aquaclear HOB filter loaded with sponges would do the trick. Removing crud before it breaks down will go farther than additional biofiltration.

Good luck,
Jim