A system for treating cellulosic fibers to improve paper, board and tissue quality; the system involves splitting fibers into an original portion having original fibers and a refinable portion. The refinable portion may further be fractionated by one or more fibers properties by a fiber fractionation system into a first fraction and a second fraction. The refinable portion as a whole, or a fractionated fraction thereof, is then refined to produce refined fibers. Varying amounts of the original unrefined fibers, refined fibers and possibly additionally fractionated unrefined fibers are blended together to form an optimized slurry that is processed by a paper machine into an optimized paper product. A master control system, fiber measurement system and optional fractionation maintenance system may be integrated with the overall system to regulate all processing.