The ceramic rings are very porous, although they look solid, there are zillions of tiny holes in it, and that makes it an ideal home for the cycle bacteria that you want in the filter. Ceramic rings are extremely porous, which provides a lot of surface area for beneficial bacteria to colonize. Due to its cylindrical shape, water flows through it easily and makes it less likely to clog. With fine and porous holes, provide the area for the autoeciousness of nitrifier, with good effect of aeration to provide oxygen for the nitrification good for decomposition of residue. Quantity half of kg of the product as shown in picture one and as written in the subtitle Picture shown for indication propose only actual product color, size may be differ due to camera effect 1kg loose repacked in a plain poly bag withought any company name or logo.