Types of filters (continued)
Wet/Dry Filters (continued)
The mechanical filtration of the wet/dry filter is accomplished by both the the pre-filter material, and the sponge that is located between the biological filter and the sump section. Because of the design of wet/dry filters, the water flow can not be restricted, so the sponges are large-pored allowing water to pass through easily. This means that the mechanical filtration is limited to removing only the larger particulate matter, and is not very efficient.
The chemical filtration is accomplished by placing a chemical media in the filter, typically in either a tray below the biological media, or against the sponge that separates the sump and biological section of the filter. Because the water merely flows through, and is not forced through the media, the chemical filtration of these filters is not very efficient.
The biological filtration of wet/dry filters is far superior to the other filters I have described thus far, for several reasons. First, the amount of surface area within the biological media provides space for the beneficial bacteria to colonize in large numbers. Secondly, not only is the oxygen content of the water very high, the media is also directly exposed to the air which allows the bacteria to be exposed to even higher amounts of oxygen. There are many types of biological medias that can be used in wet/dry filters, ranging from engineered glass and plastic products, to the use of live rock in this chamber. Again, when choosing a media for a wet/dry filter, look at the biological load that you plan on placing on the system and compare that to the available surface area of the media.
Wet/dry filters are in the high price range and require a low amount of maintenance. Because of their biological filtration capabilities, these filters have been tailored for use in most commercial applications, and are ideal for heavily-stocked fresh and saltwater aquariums. These filters are, however, not suited for a freshwater planted aquarium due to the amount of water to air contact. Again, this contact will allow most of the carbon dioxide needed by the plants to escape into the air. Although they are not very efficient mechanically or chemically, an inline canister filter can be easily added to the return line, making up for these weaknesses. Due to the nutritional requirements of the corals, in a reef aquarium, it is not always advantageous to employ efficient mechanical and chemical filtration that can remove many of the nutrients. In these situations, the wet/dry filter can be used without any supplemental filtration. The maintenance of a wet/dry filter involves weekly rinsing of the pre-filter, and the sponge located in the sump. Regular additions of fresh water need to be made to compensate for the water that has evaporated from the system. Because of the design of the overflow boxes, the water level changes in the sump, not the aquarium. It is important to monitor the water level in the sump area and not allow the pump to run dry, which may damage the pump.
Conclusion
The advancements that have been made in filtration technology over the past years have made the hobby of keeping aquatic life less of a chore, and has enabled us to maintain organisms that we were never able to in the past. Again, before making a decision as to what type of filter that you are going to install, you need to decide on the number and type of species that you plan to keep, and what their requirements are. Taking those needs into consideration, you can then look at the strengths and weaknesses along with the cost of the filtration that will suit your needs.
References and Further Reading
Delbeek, JC; Sprung, J. The Reef Aquarium Vol. 1. Ricordea Publishing. Coconut Grove, FL; 1994.
Mills, D; Vevers, G. Tropical Aquarium Fishes. Tetra Press. Morris Plains, NJ; 1989.
Mills, D. The Marine Aquarium. Salamander Books LTD. 8 Blenhein Ct., Brewery Rd. London N79NT; 1987.
