Wondering why so many find it necessary to run with two or more filters on their tanks. I've been running a single FX4 for over three years. It's running on a 72 gallon bow front. The water has always been perfectly clear and parameters right on. I do weekly water changes and clean the filter every 5 weeks. I keep spare parts in case of a break down. Such as a new pump and motor, impeller and o rings.