An undergravel filter is a very effective biological filter.  We recommend them as an important part of a successful, and low-maintenance aquarium filtration system.  We recommend that you always combine an undergravel filter with a properly sized power filter. 

An undergravel filter draws oxygenated water through the gravel.  This enables a colony of beneficial bacteria to live in the gravel bed and convert harmful ammonia into non-toxic compounds through a process called biological filtration.   We use undergravel filters in all of our freshwater tanks, and have incorporated them into our Master Kit Aquarium Sets for over 30 years.

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We use undergravel filters with AquaClear  Powerheads as part of our Master Kit Freshwater Aquarium Sets.   The picture below shows a typical setup with undergravel filter, powerhead, and external power filter.   

Aquarium with Undergravel Filter and Powerhead