Lee's Aquarium 18" x 48" Premium Under Gravel Filter - 70/90 gallon has a multi-level plate design. The larger plate sizes reduce the number of plates required. It is made of special quality plastic which resists splitting and cracking. The molded gravel guards eliminate the possibility of gravel falling down the uplift tube. The added strength of the UGF plates makes this filter most preferred by saltwater aquarist. Under gravel filter is clean and filter the water by pulling it down through the gravel, trapping contaminates in the gravel and leaving the water clear and healthful for fish. It includes premium carbon cartridges, slim discard-A-stones, telescoping ring for uplift tube height adjustment, Lee's fish-saver elbow.