Many experienced fish keepers do not use activated charcoal at all except for very limited uses. First of all, activated charcoal will only function by adsorbing chemicals for about 2 weeks give or take. After that it only serves as a structure for biofiltration. So if you are really going to use it, you need to change it quite frequently. However, many use it only for very specific tasks such as removing medication after treatment, removing discolorations and other specific impurities and do not use it any other time. It really does very little to promote the health and well-being of fish. It saves a lot of money this way. Many people are sort of intimidated into using it or have always done it and are afraid to stop, but there is little scientific data to suggest that constant usage is necessary. If you don't mind spending the money it can't hurt....but you do not have to.