Japanese mats are an excellent filter medium. Their particularly dense fiber structure ensures good water flow and a large surface area for bacteria to settle. Japanese mats do not need to be removed for cleaning if coarse dirt is captured by filter brushes. Therefore, cleaning is not necessary throughout the entire season. The mats are positioned in such a way that water can flow through them easily, preventing the filter from clogging. Otherwise, a significant portion of the beneficial filter bacteria would be destroyed during each cleaning.