If you choose to keep livestock in your pond, then it is necessary to provide some type of filtration. Of the two types of filtration, mechanical and biological,
biological filtration is what will break down the toxic products of fish and plant waste. This is accomplished through the use of bacteria. One type of bacteria use the Ammonia in the waste as a food source and excrete Nitrite. Another
type of bactera then takes this nitrite and converts it into Nitrate. This is known as the Nitrogen Cycle. Now in moderate concentrations, 30-40 ppm, ammonia and nitrite become toxic to
Nitrate on the other hand is much less toxic and concentrations in the 200+ ppm range are not uncommon, while the fish are no worse for wear. It is the Biological filter that provides a safe haven for these two distinct species of bactera. It is a home where there is a large surface area for colonization as well as a constant food source.