An undergravel filter is the original filter used by aquarium hobbyists. It is a simple design: A flat plastic dish is buried beneath the gravel. It has a tube running through it to force water to the surface. As the water sinks through the gravel, it is filtered through bacteria on the gravel surface. The clean water is then returned to the top of the tank. The system is quiet and effective. But it has experienced a slump in usage for two reasons:
Difficulty in Cleaning
Who wants to remove all aquarium ornaments, plants, and gravel and displace the tank inhabitants every time the aquarium needs maintenance? This cumbersome fact has been off-putting to many users. However, this problem has been solved through the use of a wet vac.
Fewer Tank Owners Using Gravel as Substrate
The world of aquariums has moved away from the use of gravel and toward sand, peat, and other materials.
However, the undergravel filter remains one of the most cost-effective filters on the market. So, if budget is your main concern and using gravel in your tank doesn’t bother you, this type of filter deserves a second look.