They have many patented parts and parts are replaceable. Each model is very quiet and efficient. Keep in mind that an aquarium is a closed system.
Many factors come into play.
Amount of fish, size of fish, feeding habits, etc. For maximum performance and minimum maintenance, over rather than under filtrate. Improves Aquarium Health and Enhances Biological Filtration. A Whisper 3 filter holds 2 kits. A Whisper 5 filter holds 2 kits.