Juwel filter sponges are made to fit each filter system. Use the filter baskets for your filter system to make maintenance even easier. The poly pads clean the water of large dirt particles ensuring that these do not get into the filter sponges clogging them and preventing the bio - cultures to work. Change the Poly pad in your filter system once a week. Suitable for Rio 300, Rio 400, Delta 300, Trigon 350. 5 pieces per box.