Often referred to as nitrate factories, many aquarists believe that wet/dry filters are suitable for fish-only tanks, but not reef systems. Over time the bio-material inside the wet/dry chamber becomes dirty, which eventually leads to a build up of unwanted nitrates in the aquarium, and as you should know, nitrates are not reef friendly! Therefore, to better understand this type of biological filter choice, let's take a closer look at how it works and its three basic components; the drip/trickle plate, the pre-filter (mechanical filter) set up, and the bio-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.
The Importance of a Pre-Filter Set Up
A pre-filter (mechanical 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.
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