Clay is used in ponds to achieve many goals:
Japan uses Clay in their Mud Ponds to grow up Beautiful Nishikigoi for health, colorful which they are famous for.
Montmorillonite Clay comes from one of the highest calcium clay with natural mineral already mixed by mother earth in Utah's Finest mines. There facility is mines for Food Grade Standards. Calcium based clay may help your pond water to produce some of the healthiest and deep colored koi you’ve ever raised and shown in Koi Shows.The koi’s markings will become brighter and more dominant.
Plastic pre-formed ponds, as well as vinyl, cement and rubber ponds, do not have any nutrients on their bottom. In the wild, carp use mud to get many of their micronutrients and minerals.