Quite often Air pumps are designed to become ineffectual and be replaced. However Rena do not share this attitude and believe that when a product has been underperforming, it is simply a replacement part that is needed. This is one such very important part. Use in your Rena Air Pump 100/200/300 or 400. It is easy to install and much better than buying a new pump every time. It will filter out dirt and dust preventing air-borne contaminants from being pumped into the aquarium. A discoloured pad, or a reduction in air flow, suggests that the pad needs changing.