Aquatic Arts FilterPlus Instant Upgrade Bag - 4x8 inches, Professional Grade Aquarium Filter Bio-Media, 400g (Enough for 50+ Gallons!) Provides an instant and significant upgrade to almost any aquarium filter, enabling higher stocking levels and greatly superior Bio-Filtration to Bio-Balls or Ceramic Rings. Professional grade Bio-Media for your home aquarium - FilterPlus is the only Bio-Media used by Aquatic Arts in over 150 holding tanks! Extreme surface area provides maximum surface area for growth of beneficial bacteria, enabling higher stocking levels and greatly superior Bio-Filtration to Bio-Balls or Ceramic Rings. FilterPlus is also capable of housing anaerobic bacteria, which can greatly reduce the need for water changes. Each FilterPlus Instant Upgrade Bag will filter up to a heavily stocked 30 gallon aquarium, or a medium stocked 55 gallon aquarium. Adding another bag doubles the filtration power! Completely natural! FilterPlus contains no chemicals or artificial materials. Will not alter PH or hardness, and never needs to be replaced!