Pond Blue Filter Mat Koi Media
2m x 1m mat

The mat offers a large specific area for beneficial nitrifying bacteria to establish their colonies. 
The pond mat also offers excellent water permeability. Even when multiple mats are stacked on one another, it will not affect water circulation.
Due to its high density fibers, the mat retains its shape and rigidity for a longer service life. You can cut it to whatever size you wish.