Underwater Filter Foam Inserts are designed specifically for the Fluval 2 and 4 Underwater Filter. It is an effective mechanical media that removes debris from the aquarium and encourages populations of beneficial bacteria that are important in maintaining the proper biological balance in the aquarium.
Ask a question about this product
They also provide many locations for beneficial bacteria to grow. Rinse the foam every few weeks for best results. Re-use of the foam can help protect bacterial colonies and provide continual biological filtration.