Waste-away gels continuously release good bacteria into aquarium water._x000D_ These good bacteria consume nitrates, phosphates, and organics keeping the aquarium clean and water clear._x000D_ Waste-away gels release bacteria for a period of up to 30 days and change color when they need to be replaced._x000D_ Waste-away gels are extremely easy to use, simply remove the film, attach the supplied suction cup and position the gel in your aquarium, sump or filter. Penetrates into difficult and hard to reach areas._x000D_ When it goes gray throw it away!.