Kind reminder: How often do these need to be changed? Needs to be replaced every 5 to 6 months maximum. It filters the nitrates very well if you constantly change it every 5 to 6 months. Key Feature: Sponge filters provide both mechanical and biological filtration Simply install the replacement sponges into the arms holding the sponges The sponge traps larger waste particles mechanically cleaning the water without trapping baby fish It works efficiently and quickly to clear the water Ribbing shape sponge has a lot of surface area for growth and breeding of beneficial tiny creatures Easy to clean: remove the sponges to clean them, soak gently in a container of tank water. Do not use untreated water and do not agitate it a lot or you will lose the beneficial tiny creatures Useful for as breeding filter or as secondary filter