Previously I had always turbid yellowish water in my 325 liter aquarium. Since I use this filter material I have crystal clear water and the fish (rainbow fish) you can see it well on the Like it. I call biological filtration, Cirax provides for beneficial bacteria a huge settlement surface. After about a year you should replace it. It is delivered in a properly fitting filter basket, you need it only push into the filter and you're done. I'll buy it again and again.
