I never trust it to be enough. I have a couple of the whisper filters that still have the original nasty cartridge in them after several years. The carbon in the whole cartridge is probably less than an ounce so it is a carbon filter in name only. I got a refillable cartridge for one of them so I run it empty of any carbon media. The bioload in that tank is always low so I don't fret not having more media in the filter.