I havent used carbon in my tank since I got that first carbon package with my new filter. I hear that activated carbon only works for like 2 weeks an dit gets expensive if you really keep up with it. All I use iis my sponge an dI clean it out every so often. Is this bad/good for my fish or what? I havent lost one fish in my tank due to the paramaters. I have hadseveral fish killed in my tank but not just up and die for noe reason. Am I overlooking something or is having carbon in the tank a good thing??