The air injected into the chimney is transformed into micro bubbles which, when rising, generate suction through the foam located at the base of the filter. the gentle suction of exhaust filters protects young fish and shellfish from the deadly suction of electric propeller filters. In addition, the micro-fauna develops on the moss and the food trapped by the filter remains accessible to the animals, guaranteeing healthy growth and water with less nitrogenous waste. Your purchase is therefore covered by the "Paypal Purchase Protection: If you do not receive your item or service or it does not correspond at all to its description, you are covered for the total amount of the transaction, including costs return (see Paypal Terms and Conditions). I will send the items as soon as payment is re.