i dont think carbon will leech off chemicals as much as it would stop working effectively. Carbon has a certain volume of impurities it is able to collect, onces its topped off, it simply stops working. Hence the month long life span. Chemical filtration like carbon, ammonia resins, and phosphate removers are good for an overnight fix after slacking on maintenance. Other than that, its not cost effective or necessary to use all the time. I would personally load up on lots of biological filtration. And if you have the budget to get another fx5, DO IT!