| 摘要 |
<p>A filtration unit (10) for an aquarium tank comprises a biological filter chamber (11) which is cyclically exposed to air and water without the use of conventional syphon means. Alongside the chamber (11) is a U-tube arrangement (25) one branch (27) of which communicates at its upper end with the upper region of the chamber (11). Compressed air is continuously admitted to the chamber (11), e.g. by bubbling up beneath its open bottom end. When the water in chamber (11) drops to the level of the bend of the U-tube (25) air in chamber (11) expells remaining water from the U-tube and is able to evacuate chamber (11), enabling it to refill with water. <IMAGE> <IMAGE></p> |
