These Replaceable Filters are easy to clean and durable for long-term use. Bio Balls Filter great for fish tanks, are especially suitable for freshwater fish tanks, marine aquariums, aquaculture, waste systems, fish hatcheries and more, to promote gas exchange and increase the proportion of oxygen levels. Features -Color:Black -Material:PVC -Size:2.60X2.60X2.60cm/1.02X1.02X1.02in -The Filter Balls are easy to use, improve circulation and filtration, has a lower filtration pressure and a rate. -The internal biochemical cotton further improves the filtration effect and stabilizes the quality, accelerating the maturation of nitrifying . -The Aquarium Algae Filters that are not easy to invalid can be treated by adsorbing oil and other impurities. -The Filter Media are compact, are not easy to accumulate, long working cycle and have low loss. -With multiple plastic skeleton, large surface area for the growth of nitrifying . Package list: 250 x Aquatic Bio Balls