Wet/Dry Trickle Filter: A Guide
A wet/dry filter trickles water over air-exposed media so aerobic bacteria get maximum oxygen, giving strong biological filtration.
Compiled by Aquairi from published sources · Published
Overview
A wet/dry filter, also called a trickle filter, is a sump-style biological filter in which water flows over media that is exposed to air rather than fully submerged. This air contact supplies abundant oxygen to aerobic nitrifying bacteria, making it a strong choice for aquariums with a heavy bioload such as cichlid or large predator setups.
How it works
Waste-laden water is delivered onto a drip plate and trickles down through media that stays wet but not submerged. As the water cascades over the media it releases carbon dioxide and absorbs oxygen from the air. A biofilm of aerobic microorganisms growing on the media oxidizes ammonia to nitrite and then to nitrate.
Media
- Plastic bio-balls with a high surface-to-volume structure
- Filter wool or pads for mechanical pre-filtration
- Other porous biomedia with high surface area
Why air exposure matters
Nitrifying bacteria are aerobic and consume oxygen as they process waste. Because the media in a trickle filter is exposed to air, it receives far more oxygen than fully submerged media. As a result, trickle towers process ammonia faster than submerged filters and offer very high biological capacity.
Limitations
A wet/dry filter excels at biological filtration but is often described as a nitrate factory because it converts ammonia and nitrite efficiently while doing little to remove the resulting nitrate. The open trickle chamber also increases evaporation, and mechanical pre-filtration must be handled by separate pads that clog over time.
Maintenance
Mechanical pre-filter pads are rinsed or replaced frequently so trapped debris does not decay on the biomedia. The bio-balls themselves are rarely disturbed, since aggressive cleaning removes the bacterial colony. Topping off evaporated water keeps the system level stable.