Replacement sponge for aquarium filter Fits the AF-400 Aqua Della filter Description: Replacement sponge for the Aqua Della filter AF-400 and the older model AFI-250. This sponge is the first step in the filtering process and ensures that coarse particles are removed from the water. This keeps the water clean and clear. The sponge is easy to remove from the filter for cleaning. For optimal operation, it is advisable to replace the sponge once every 90 days.