This Pisces foam is a perfect replacement for use in the Hozelock Bioforce 4500 pond filter. Each foam pad is 19 x 7 x 5cm. The foam can simply be added to the pond filter system when needed. Made from long lasting materials, the foam has a large surface area to help to effectively catch debris to produce clear water. The foam pad has a porous structure that is a perfect habitat for beneficial bacteria to work hard to remove impurities in the pond water. It is recommended that filter foams are replaced every 6 months to ensure the pond system is kept at its best.