You missed the part about filters removing large particles before they break down. The skimmer removes the next smaller stage ( proteins/fats) and then the algae in the fuge uses the smallest (individual molecules) for growth. The order of the skimmer/algae doesn’t matter as they get plenty of repetitions to remove something. By contrast the mechanical media gets one time to either catch the particulate or have it pass through. If it can get through once and break down, it normally will again. By removing the big stuff at the beginning, the other two don’t have to work as hard.