Clean water leads to healthy, happy fish. Changing the carbon filter on a regular basis helps provide the environment they need to thrive. Part of maintaining the best aquarium water quality you can is replacing the filter cartridge as soon as it's needed. You've already made a strong choice in purchasing a Whisper EX filter and your fish appreciate it, so keep a stock of these carbon filters near by and use the indicators provided to ensure the healthiest, highest quality life you can for your fish. These Tetra Whisper carbon filters made for the Whisper EX30, EX45, and the EX70 have three important parts of their protection package: Coarse layer - Removes larger particulates. Activated Carbon - Rapidly removes odor, discoloration, impurities and toxins leaving your water clean, healthy, and polished. Multi-density layer - Specially designed to capture a full range of particulates giving you unmatched water clarity. Losing track of time is not an excuse anymore! These carbon filters come with Timestrip and take any guesswork out of carbon filter usage. Just place the Timestrip into your Whisper EX system, activate it by pressing the start button, and when it turns red replace both the filter and the Timestrip. Super easy. Manufacturer recommends if your aquarium contains a large number of fish or live plants, then consider purchasing the next size up filter and cartridges.