Recommended every time the water is changed. For clearing organic waste from the aquarium bed. By adding an extension piece to the gravel washer, the aquarium bed can be cleaned deeper. Light bedding substrate is not so quickly and unintentionally sucked away. Regular usage prevents poor water values. Tips on water quality: Each time you change part of the water, useful bacteria are also removed from your aquarium. These bacteria are important for breaking down harmful organic contaminants. By adding HOBBY Bacteria Fit each time after a water change, the balance of useful bacteria can be maintained. If you have persistent algae problems despite changing the water regularly, this may be due to a high nitrate content in the aquarium. The source might be a biological imbalance caused by too much food, too many fish, not enough plants or tap water containing excessive nitrates. In such case we recommend HOBBY Nitrat-Killer. Through ion-exchange, this product quickly draws nitrate out of the water, without re-releasing it into the water. HOBBY Nitrat-Killer can be regenerated for repeated use.