How Does a Wet/Dry Filter Work?
A basic wet/dry trickle filter consists of vertically passing filtered aquarium water over an exposed filter media, then into a receptacle, usually a sump. As the water passes over the filter media, the ammonia and nitrites in the water are processed by the resident nitrobacter and nitrosomona bacteria into nitrates. As the water passes over the filter media, it is exposed to air, allowing the free exchange of gasses (O2 & CO2). The rapid oxidation of ammonia and nitrite makes these filters extremely efficient; they are an outstanding choice for freshwater and saltwater aquariums. Wet/dry trickle filters also help keep the dissolved oxygen (DO) level in your aquarium water at a high level.
The Importance of a Pre-Filter Set Up
In order to keep the filter media from clogging up with debris (uneaten food, detritus, etc.) from the tank, it is important to filter the water before it is passed over the media. If material remains in the media for long, it will start to decompose, creating nitrates. Rightly or wrongly, bio-balls and the like have long been know as "nitrate factories, due their tenancy to trap particulate matter from the tank water. Mechanically filtering the water to remove particles before it reaches the filter media will greatly reduce bio-material clogging.
Most wet/dry trickle filters are used in conjunction with a sump. The Berliner WD-125 Wet/Dry Filter is a good example of most wet/dry filters used today. Felt pads are frequently used above the filter media with good results. These reusable pads are easily removed to be rinsed, then replaced. The felt pads are available in several densities.
About Choosing a Bio-Material
While most wet/dry trickle filter manufacturers recommend their own brand name materials, there are a number of biological filter media materials which will work well in almost any wet/dry unit. From "Bio Barrels", to "Bio Pin Balls", to "Bio Balls" to "Biological media Balls", to "Ceramic Rings" (and many more), there are many forms of biological media material on the market today. Each has its own properties and offer different features. Some contain more surface area per cubic foot (biological filter) while others are more open and will aerate the water better (gas exchange). The media with more surface area tend to clog faster, which can increase maintenance. The cost per cubic foot difference of each material is quite amazing. If you are starting a new wet/dry trickle filter or replacing the material in one, make sure that you do the research before purchasing and material.
In spite of all of the pre-filtering that you might do, there will come a time when you may have to clean your bio-material, in order to keep them from becoming a "nitrate factory". Since cleaning your bio-material will result in a temporary loss of the resident bacteria, you might want to consider cleaning only a portion (perhaps ¼ or 1/3) of the bio-material at one time.
About Removing the Bio-Media
With the desire to attain a "natural" reef system, or that unwanted nitrate will become a concern, often aquarists will completely remove the bio-media from the wet/dry filter chamber AFTER their system has become well established and convert it into a sump box, allowing the live rock and sand to become the main biological filtration source. This can be done, but ONLY by removing about 1/4 of the media at any one time in at least 1 week intervals, testing for the appearance of ammonia in between to assure that the system is remaining stable during the elimination process of this biological filtration source. If ammonia does appear, DO NOT remove any additional media until the level drops back to zero, and then only continue on after waiting several weeks to allow the nitrifying bacteria population to build up again. It is important NOT to add any new livestock to the system during this transition period as well. In our opinion a wet/dry trickle filter is an efficient biological filter choice, but only if it is properly maintained and other regular aquarium maintenance and water change routines are followed.