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.