Filtration is probably the first and most common downfall for the Goldfish hobbyist. The primary reason is that Goldfish are fun to feed, they can eat a prodigious amount of food if allowed to do so, and the concomitant wastes, which the Goldfish produce, present a challenge to any traditional filtration scheme. Filtration occurs on two levels. The first level is the mechanical phase in which visible impurities and particles are removed by a mechanical baffle or screen. The second level of filtration is the actual chemical reduction of waste in the water. In this discussion, we are primarily concerned with the elimination or reduction of nitrogen from the water. The nitrogenous waste products come from the proteins that the fish ingest, and is liberated into the environment in the form of Ammonia, which is reduced by bacteria living on the surfaces of the filter media. We will discuss this again, in more detail, in the section on “The Cycleâ€