Clinofish Koi Filter Sand is a type of Zeolite mineral, mined in South Africa. The mineral searches for and collects toxic ammonia from pond water, acting as a filter on the atomic scale. The powerful negative charge attracts positively charged cation contaminants, such as ammonia, and holds them in its large surface area, unlike the alternative sand or glass, which traps particles between the grains. Clinofish Koi Filter Sand reduces fish mortality rates, improves water clarity, eliminates excess algae and is a 100% natural mineral, which can be reused multiple times. The amount of Clinofish Koi Filter Sand required will be determined by the size of the pond filter. The average pond filter will require 2 x 25 litre bags of Clinofish Koi Filter Sand.