In front of the Eheim's will be two spin down filters (centrifugal filter with a screen) in series, the first with a 74 micron screen and the second with a 30 micron screen. After the Eheim's a washable 5 micron filter followed by a disposable 1 micron filter before the UV and pump. I thought it might be simpler and more economical to do it this way. Also, it may help to maintain or increase the flow rate.