The check valves as shown pose a lot of back pressure. I guess this could be over come with adjustment of the valves, however, if it were me I would loop the reactor and uv sterilizer from the sump. I just have a problem of valving down the gravity drain as it is a formula for desaster if anything clogs or slows down. tank over flow. With a loop system from the sump you can do away with the check valves and use the other valves to control flow. In short your present design poses a potential for overflowing the main tank. good luck keep us posted.
