Hobbies And Interests
Function
The UGF is placed under about two inches of gravel spread to cover the bottom of the tank. The filter, operated by an air pump, air stones or a powerhead, pulls water down through the gravel, which then traps contaminants.
Maintenance
UGFs need regular maintenance to remain unclogged and effective. The dirt sitting on top of the filter plate under the gravel must be removed, usually with a special siphon available at pet stores. Also, the air stones, tubing and pump diaphragm need periodic replacement, according to Timothy A. Hovanec, author of "Which Filter to Choose."
Considerations
A UGF is most effective for tanks under 55 gallons in size. The filter can be combined with a prefilter, such as a power filter that hangs on the tank's edge, for a more complete system. Some hobbyists skip the UGF and just opt for the other filter because they require less maintenance while keeping the water clean.