Penn Plax Small World Fishbowl Filter KitThe Penn Plax Small World Fishbowl Filter Kit is designed for round or drum fish bowl or tank containers with at least a 4 inch opening. Once assembled, simply place the filter inside your completely empty aquarium, cover it with your choice of gravel, marbles or stones, and then fill it with water. You can also adjust the air flow on the Penn Plax Smallworld filter kit with the included air valve. Filter kit includes: adjustable filter plate, lift