I use the Black Diamond Carbon when I think my water looks a little yellow. Usually for a few days every month or two. Sometimes I put it in the media tray of my sump , so the drain water passes through it, and other times I just toss it in my sump ( I know I probably shouldn't do that). I take it out when I don't notice the yellow tint to my water anymore, or when I remember. Eventually, I think I would like to run it through a some sort of a reactor. I hear a lot of people have good luck with using phosphate reactors to run carbon.