eBay

Size: 3.9" x 3.9" x 1" / 2 blocks
Vast surface area / porous internal structure results in superior efficiency
Technology each Brick contains over 5.5 million NanoSpheres
The three-dimensional pores produced by each piece.
Bio Filter Brick media suitable for all kinds of aquarium tanks.

Hipanda Aquarium Ceramic Plate Bio Filter Media 2 Pcs,Biological Filter Brick for Marine and Freshwater Fish Tank