A flow-through filter is fed by the pump in the water. The filter is the highest point in this cleaning cycle; from this point the water then flows back into the pond. Then the sponges in the interior of the filter take over the function of cleaning the water. After a period of time this is where industrious microorganisms form that decompose the excess nutrients in the water. The advantage of flow-through filters: They are easy to reach, they are above ground. Cleaning and maintenance are quickly executed.