Mechanical Filtration

The main function of a mechanical filter is to remove large particles from the water before they begin to decay. This helps to reduce the amount of substrate or "stuff' available for mineralizing bacteria to convert into ammonia and other substances. The mechanical filter could be considered equivalent to the currents and tidal flushing on a natural reef, as both help to remove particulates. The key to proper mechanical filter design, if one is used at all, lies in regular cleaning. The easier it is to clean, the more likely you are to clean it on a regular basis. Frequent cleaning of the mechanical filter helps to maintain a high redox potential (Paletta, 1989), which is one of the keys in preventing microalgae problems. Mechanical filters come in a variety of designs, though not all of them are well-suited to reef aquarium husbandry. Common materials for reef aquarium mechanical Alters include sponge pads, fibrous mats, or polyester floss. Rapid sand, pleated cartridge, and diatomaceous eaith filters are best suited to fish systems, or only for temporary use on reef aquariums. Mechanical filtration is not absolutely necessary for reef aquariums, as we will shortly explain

One feature of European aquaristic that has gained prominence in North America is surface skimming. This is the process whereby wTater is drawn off the surface of the aquarium, resulting in a clean water surface, and enhanced gas exchange and light penetration. Surface skimming is accomplished by the use of an overflow design that may incorporate some form of mechanical filtration. With this design one can efficiently remove floating particulate matter and dust that settles on the surface, and even some amino acids and fatty acids that collect at the surface because of their polar nature. Early designs consisted of an overflow located in one corner of the aquarium. A stand pipe was fitted into a hole drilled into the bottom of the tank behind the overflow partition, and some type of filter padding was wrapped around the pipe. A problem with this design is that the aquarium hood and/or lights have to be removed to get at the pad. Another problem occurs in tall aquariums w hen animals or pieces of equipment fall into the overflow. They are difficult to remove. Since such overflows are difficult to service, they tend to be neglected and gradually become clogged. One then sees overflows filled with water circulating around a stained filter pad. "Conversion" units,

designed to hang on the back side of the aquarium have also come onto the market. Operated by a siphon, they eliminate the need for drilling holes in the aquarium, and allow you to easily convert an aquarium to surface skimming, with a trickle filter or a reservoir below the tank. A mechanical filter can be located either in the overflow box or in the top half of the trickle filter or reservoir, and it can be cleaned without disturbing the main tank. However, siphon boxes are not without their problems. If they become clogged or lose siphon, your tank may overflow onto the floor. If you change water pumps you should check first to see if your siphon can handle the new flow rate. An alternative to the above designs is to use a hole drilled in the side of the aquarium near the upper rim, fitted with a bulkhead fitting. By constructing an overflow partition in front of the hole, you can make an easily

In this simple sump, a plastic basket serves as a diffuser to slow the rushing flow of water draining down from the tank. A larger basket could be employed to hold mechanical filtration media, i.e. floss. Note the activated carbon located in bags outside of this basket. The bags of carbon can be located in a basket as well, but must not be placed where strong water flow will cause the carbon grains to tumble and disintegrate. Also note protein skimmers located in sump. J. Sprung.

accessible chamber. You must ensure that the size of the hole is large enough to handle the anticipated flow rate. We recommend a mechanical filter basket with polyester floss just where the water enters the sump, if you use a mechanical filter at all. This design simplifies filter changing and inspection compared to location in the overflow chamber. We recommend that you avoid the use of pleated cartridges and canister filters for mechanical filtration in reef tanks since these are unlikely to be serviced frequently.

Mechanical filtration can be accomplished more passively, by settlement in the sump or a connected "refugium" aquarium. If the sump has a sloped bottom, then particulate matter will settle at the low end where it can be removed by siphon or by means of a purge spigot installed there. When combined with surface

Sump Filter Design


skimming and a good foam fractionator, this design avoids the need to bother with cleaning and replacing mechanical filter media. In fact, in a reef aquarium it is not necessary to use any mechanical filter media at all. Mechanical filters trap amino acids and carbohydrates in addition to particulate matter, and all of these things are decaying there with the entire volume of the tank flowing over them. The advantages to avoiding mechanical trapping media are that more particulate matter is available for filter feeders, and more surface active material remains in the water, which enhances the performance of the protein skimmer. The particulate material left in the water also supplies a source of organic food for the heterotrophic denitrifying bacteria living in the substrates (rock, sand, gravel). However, without good circulation and the inclusion of bottom stirring creatures, the particulate

Figure 5.1

Settling filter

After Van Der Elst, 1993,

Partition Type Sand Filter

detritus can accumulate and lead to algae blooms. As a general maintenance procedure, occasional "blasting" of the rocks with a powerhead or baster will prevent the formation of heavy deposits of detritus. This simulates an effect of storm surge on the reef. A mechanical filter can be installed just for this maintenance procedure, to be performed about every six months.

Biological Filtration

Biological filtration refers to the biological processes that occur in aquaria where waste products are mineralized and oxidized by various types of bacteria into less harmful products such as nitrate (nitrification), or reduced into nitrogen gas (denitrification). By using bacteria in this way we emulate parts of the biological cycles that occur on true reefs (see chapter 2).

One of the most common fonns of biological filtration is the undergravel filter (UGF). You can keep a reef tank with a standard

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