This product effectively removes nitrate from your aquarium therefore dramatically improving conditions for both fish and plants. Less nitrate means less algae, better plant growth and healthier fish, all the things we strive for as fish keepers. The sponge contains microbes which consume the nutrients that algae need to survive, the algae consequently die through starvation. Check the nitrate level in you aquarium before application with an appropriate nitrate test kit. Once you have the initial reading, check the nitrate level every few days and once it reaches zero the algae will disappear.Before using please remove the outer packaging. Application is simple: just remove on of the upper coarse blue sponge and replace it with the new green Juwel Nitrate Removal Sponge.The Juwel Nitrate Removal sponge will reduce the nitrate to zero, test the water regularly to monitor nitrate levels and change the sponge every 8 weeks to maintain optimum conditions in the aquarium. 1 piece in each box.