Wet/dry filters have been a very popular choice in biological filtration for a very long time in the saltwater hobby. However, as the technology in aquarium keeping has advanced, and the desire to attain a "natural" system becomes ever popular, much controversy surrounds this choice.
Many aquarist's believe that this type of biological filter is suitable for a fish-only tank, but not for a reef tank. Often wet/dry's are referred to as nitrate factories, because over time the bio-media material may become dirty and this eventually can lead to a build up of unwanted nitrates in the aquarium, and as you should know, nitrates are not reef friendly! To better understand this type of filter, let's take a closer look at how it works and its three basic components; the drip/trickle plate, the pre-filter, and the bio-media material used inside.
How Does a Wet/Dry Filter Work?
There are many designs to choose from when it comes to wet/dry filters, but they all work on the same concept. A wet/dry filter, also referred to as a trickle filter or a bio-tower, is an aerobic filtration method. For those of you that may not understand the term aerobic, it means occurring or living ONLY in the presence of oxygen. In other words, it can only work when oxygen is present. For this type of filtration, the more oxygen saturation it gets, the better it functions. 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.
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