A great benefit of the Aqueon QuietFlow filters is the internal pump design that helps dampen noise, eliminates leaks and because it is self-priming, starts up automatically after cleaning or power interruptions. Higher flow rates also ensure a higher dissolved oxygen content for healthier, more active fish. There are five total stages of filtration–mechanical, chemical, biological and an additional specialty pad–for the cleanest, clearest, healthiest water. Stage 1 – Dense floss removes particles and debris. Stage 2 – Activated carbon removes toxins, odors and discoloration. Stage 3 – Patented Bio-Holster removes toxic ammonia and nitrites. Stage 4 – Diffuser grid removes additional toxins while adding oxygen for more active fish. It also reduces splashing makes the return exceptionally quiet. Stage 5 – Specialty filter pad option for additional carbon, ammonia reducer or phosphate remover. All filters use Aqueon Replacement Filter Cartridges and Aqueon Specialty Filter Pads. Fits aquarium size up to 20 gallons LED indicator light flashes when it's time to change the cartridge Filter pump is self-priming, just plug and play out of the box; filter will auto-restart if power is interrupted and restored Provides mechanical, chemical, biological, and additional specialty pad filtration High flow rates ensure a highly dissolved oxygen content for healthier, more active fish