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Wet/Dry Trickle Filters

A long-standing choice in saltwater biological filtration, wet/dry trickle filters are now becoming a source of controversy with the ever-increasing popularity of reef systems. Long thought to be fish, but not reef, friendly, aquarists often think of wet/dry trickle filters as "nitrate factories". Over time the biological media inside the filter becomes dirty, which will cause a build up of unwanted, reef-harming nitrates within the aquarium. However, with research and understanding, trickle filters can be an asset to any aquarium. Although there are many variations of wet/dry filters, they all operate using the same basic concept: aerobic filtration. "Aerobic" implies that the process can only take place in the present of oxygen. Therefore, the more oxygen saturation this system has, the better it works. Water is pumped from the aquarium, then by means of a drip/trickle plate or rotating spray arm the water is dispensed or "trickled" down over and through a biological material source contained in the wet/dry filter chamber, but not before the water is pre-filtered by means of mechanical filtration, which can be accomplished with the aid of a protein skimmer or by placing a pre-filter material such as filter floss, a filter sponge, or micron filter felt on top of the drip/trickle plate area. When the water falls through the holes of the drip/trickle plate onto the bio-media, this allows for aggressive oxygen saturation of the water. Remember, aerobic! The clean filtered water is then deposited back into the aquarium either directly, or first into a sump or some type of water containment area and then returned. The Importance of a Pre-Filter Set Up A pre-filter set up allows the tank water to be cleaned of excess debris, particulates and other unwanted organics (DOCs or dissolved organic compounds) before it passes through the bio-media in the wet/dry chamber. By using this process it helps to prevent the bio-material from getting clogged and dirty, as this is what can contribute to the build up of nitrates in an aquarium. A double drip/trickle pre-filter plate design, where one plate drips down onto the other, can also be incorporated. The first plate holds the pre-filter material on it, and the second is just a plain drip plate. It is important to keep the pre-filter material changed. The purpose of the pre-filter is to only collect unwanted junk in the water, and nothing else. If the pre-filter material is not maintained regularly, this can decrease the flow rate of the water that trickles into the wet/dry filter, in turn decreasing the oxygen saturation level. This also allows the pre-filter material to act as a contributor to the build up of unwanted nitrates in the aquarium. The frequency that you change the pre-filter material depends on the animal and feeding load you have on your system, but no less than a weekly change is recommended, and it definitely should be changed when it begins to turn brown. About Choosing a Bio-Material Just about anything can be used as a biological filteration material, but ideally you want a type of media that has a large surface area for growing bacteria, does not compress down, is saltwater friendly, and has good water/oxygen exposure around and through it. The top choice bio-media is usually in the form small spiked plastic balls, or bio-balls, but there are many other types of bio-media one has to pick from (see Choosing a Biological Filtration Material). Some commercially sold wet/dry filt

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