Featured is a LED filter cartridge change indicator light that flashes when the cartridge becomes clogged with debris, providing a reminder that it's time to replace the cartridge. A great benefit of the Aqueon QuietFlow filters is the internal pump design that helps dampen noise, eliminates leaks and is self-priming, meaning it 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 provides surface area for beneficial bacteria that remove toxic ammonia and nitrites. Stage 4 – Bio-Media grid supports additional beneficial bacteria establishment while adding more oxygen. It also reduces splashing making 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. QuietFlow LED Pro 10 – Medium cartridge. QuietFlow LED Pro 20, 30 and 50 – Large cartridge. QuietFlow LED Pro 75 – two Large cartridges. Change filter cartridge every 4 weeks for best results.