The two pack of Fluval Bio-Foam Max 407 provides incredibly effective biological filtration for freshwater and saltwater environments. The foam sponge was designed with rippled surface pattern that offers 30% more area to quickly and efficiently trap dirt, waste and debris. This surface area is the ideal breeding ground for beneficial nitrifying bacteria to improve the quality of your water. The foam helps to reduce the amount of premature clogging and extends the life of filter media as well as providing an improved water flow. Fluval Bio-Foam Max 106/107 is designed with a perfect fit, so there won't be any gaps or spaces that contribute to a lower filtration efficiency. Replace every six months.