Biological filtration
From Koipedia
Biological-filtration means we combine oxygen, solid surface area, water and organic matter. The goal is to break down the organic matter, through what is called the Nitrogen_Cycle, into less harmful end result of nitrate. One of the keys to Biological filters is to remove as much as the organic material as possible before the water is introduced to the Bio filter using Mechanical_filtration.
Types of Biological-filtration common in Koi ponds:
Foam / Brushes / Matala / Sponge
Boyant media - Kaldnes, bioballs etc.
Sand / Gravel
Trickle towers (TT)
Pond bottom, plumbing and rocks also offer some limited bio filtration
