The only time I ever had my XP's lose flow is when the filter is plugged. If you have a lot of gunk in the tank, or overfeeding, the micropad will get clogged pretty quick. Also, gunk can get built up in the impeller shaft area, slowing or stopping the impeller, but that doesn't hapen much, unless you aren't cleaning the impeller with your maintenance. It's easy to clean, just unscrew the cover under the bottom side of the XP cover and remove the impeller, and clean off the impeller as well as the hole where the impeller goes. Any small brush will work for doing this.