Penn Plax Small World Filter Cartridges (2 pack) suitable for the small world filter, The Smallworld Filter by Penn Plax is an ideal filter for all small aquariums up to 20 litres. This filter helps to remove harmful gasses, odour and discolouration and is quick and easy to install. Included with disposable carbon and sponge filter cartridge, tubing and adjustable air valve, and suckers. Suitable for all small aquariums. Measures approx 15 x 13 x5 cm.