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Trickle or Wet/Dry Filters

Filtering Your Aquarium Water

(The First Tank Guide)

What Is a Trickle Filter?

Trickle filters are aquarium filters that remove the water from your fish tank by means of an overflow and allow it to fall through or over filter media in an open tower to be collected in a sump, and then pump the water back into the tank through a spill way or spray bar.

How Does a Trickle Filter Work?

Trickle filters allow water to freely flow out of the tank by means of an overflow. As the name implies, an overflow is a mechanism that allows water to just flow out of the fish tank when it reaches a certain level. Overflows are also used in swimming pools and reservoirs to control the water level and when and where water flows out of the pool or reservoir. In the case of a trickle filter, once the water flows out of the main tank by means of the overflow, it is collected or channeled into a drain pipe.

The drain pipe channels the water to the top of the tower. At the top of the tower is a spinner, spray bar, or distribution plate. A spray bar is a horizontal tube with holes in it to spray water across the top of the tower. A spinner is just a spray bar that rotates. this rotation is usually provided by the water itself, either coming through a screw or impeller to get to the spinner, or because the holes are all on one side of the tube and the water spraying out of the spinner pushes the spinner back the other way slightly. A distribution plate (or drip plate) is just a plate of aquarium safe plastic of acrylic with holes drilled into it to allow the water to drain in many places.

Trickle Filter Diagram The spray bar, spinner, or drip plate spreads the water out across the top of the tower more or less evenly. The tower is called a tower because it is usually relatively tall and narrow and rises above the sump.

The water the "trickles" through the biological filter media drawn downward toward the sump by gravity. As the water flows down through the media, it is exposed to free-moving air, which keeps the water oxygen rich. The high oxygen levels in the water in the tower improves the efficiency of the nitrifying bacteria providing biological filtration.

Once the water has passed through the filter media, it falls into a holding area, the sump. The sump is just another tank to hold water. This allows for the water level in the entire system to vary somewhat, while keeping the fish tank full and the overflow working.

Water is pumped from the sump back into the tank, forcing more water over the overflow and through the tower. Trickle filters always use water pumps to move water, most models require that the pump be purchased separately.

What Maintenance Does a Trickle Filter Require?

There is very little maintenance required for a trickle filter. Periodically, excess debris should be rinsed off the bio-media to keep the passages through it from becoming clogged, and the tubing and pumps will need to be kept clean and free of debris.

Using a mechanical filter in conjunction with your trickle filter will reduce the need for rinsing the media, as long as the mechanical filter is cleaned regularly.

What Should I Be Aware Of with a Trickle Filter?

Trickle filters provide excellent biological filtration, but do not do much for mechanical or chemical filtration.

Trickle filters are really only appropriate for large fish tanks (about 80 gallons or more) or centralized filtration systems for multiple aquariums, due to the high flow rates of appropriate pumps and the additional expense and space required for the plumbing and sump.

Recently smaller fish tanks (10-60 gallon) have become available with integral trickle filters.

The high cost of setting up a trickle filter is often prohibitive to the beginning aquarist.

Remember, trickle filters do not provide mechanical or chemical filtration for your aquarium.

Another disadvantage to the trickle filter is their high rate of evaporation. Though not as high as a comparable sized power filter, and no where near as high as a comparable capacity rotating drum filter, the evaporation rate is a consideration when maintaining a trickle filter.

Why Are Trickle Filters Sometimes Called Wet/Dry Filters?

Well, trickle filters are called trickle filters, because the water trickles down through the tower, assisted only by gravity.

But why are they called wet/dry filters as well?

Actually, wet/dry filters are a subset of trickle filters. Some trickle filters are fitted with mechanical and/or chemical filtration cartridges in the sump so the water has to flow through this additional filter media before being returned to the fish tank.

Since this additional filter media is in the water and is "wet," and since the tower and the biological media are above the water and "dry" (well, not really, but whatever), part of the filter is wet and part is dry, hence the term "wet/dry filter."

"I've had 30 and 50 gal freshwater units for a couple of years now but wasn't aware of some of the interesting things you pointed out in your segments, [especially] concerning substrate and filtration."
May 6, 2002
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"Thanks Keith! I will give it the old college try! I sure am glad I found your web site!!"
February 19, 2002
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