Internal Aquarium Power Filters Interpet Model:PF3 Internal Filter Smaller particles down to 2mm Smaller particles down to 2mm in size can be eliminated by fitting the supplied clip in fine mesh filter tray which affords the best possible protection for pond wildlife such as small fish please see the column in the specification table regarding maximum replacement bulb length as these filter sets take only specific sized bulbs and anything longer than stated will not fit inside the system Filters help to remove toxic compounds such as Ammonia from the water which can end up being very lethal to your fish and live plants if untreated The Biochamber which houses the bio media (included) is used for allowing beneficial bacteria to grow and thrive inside of the filter which helps to break down Ammonia levels in the tank