Penn-Plax Filt-a-Carb Universal Carbon Undergravel Filter Cartridge, 3 Packs of 2 each

The Penn-Plax Filt-a-Carb Universal Carbon Undergravel Filter Cartridge comes in a pack of 3, with 2 cartridges in each pack. The cartridges fit well in undergravel filters for tanks ranging from 10 to 55 gallons. They are nicely made and work well to keep aquarium water clear, lasting about a month before they need to be replaced. The charcoal filters emit more bubbles than the standard filters that come with the tank, which is preferable for some users. The undergravel system is also Considered better for guppies as it is less strong, so it does not suck up baby fish. However, some customers had difficulties installing and trimming the tubes to fit properly, and some received the wrong cartridges that were not compatible with their set-ups.