Nano Cube Replacement Sponge Filter Media Fits MT-40 and 402-12 gallon Nano Cubes. Provides mechanical filtering of solid waste matter from your aquarium water. Prevents early clogging of other filter media in the filter path. Sponge Filter Media should be replaced every 2 months. Alternate the replacement of the sponge with activated carbon to maintain biological filtration. Nano Cube Replacement Ceramic Rings Fits all Nano Cubes. Ceramic Rings for the Nano Cube are ideal for fostering beneficial bacteria. Be sure you do not change the ceramic rings at the same time as bio-balls, sponges, or carbon media. Doing so could remove too much of the positive bacteria in the tank and cause rising levels of ammonia. Nano Cube Replacement Activated Carbon Filter Media Fits all Nano Cubes. Activated Carbon absorbs impurities in your aquarium water. It removes dissolved organic waste that can stress tropical fish and discolor your aquarium water. Safe for both fresh and saltwater aquarium environments. Replace carbon every 3-4 weeks to avoid leaching of the contaminants back into the tank.