Building a Wet-Dry Filter on a Dime

Building a Wet-Dry Filter on a Dime.

A wet-dry, or trickle aquarium filter is very simple in concept: when you drip water on a medium with large surface you create a thin layer of water which easily saturates with oxygen from air and supports microorganisms, primarily bacteria, that transform harmful ammonia and nitrites into less toxic nitrates. Nitrates can in turn be used by live plants and algae in the aquarium. Wet-dry filters are suitable for both freshwater and saltwater aquariums. In recent years a more efficient method of removing nitrogen from saltwater aquariums has been devised: a protein skimmer. At this point, protein skimmers pretty much replaced wet-dry filters in saltwater setups. Unfortunately, protein skimmers only works in salt water, which leaves wet-dry filter as the best method to rid freshwater aquaria of nitrogen-containing byproducts.

The main part of the wet-dry filter is basically a container of material with large surface-to-mass ratio, through which aquarium water is dripped. This material can be a bunch of synthetic fibers or so-called "Bio-balls" specifically designed for this purpose. It is usually a good idea to include an easy to clean mechanical pre-filter in the design to catch large debris that can clog the system. There are multitude of option for building your own or buying a pre-made main filter chamber. I made mine for about $25, of which $16 were bio-balls. Click here for detailed instructions on how to build your own with pictures.

If you can place the main chamber of your wet-dry filter above your aquarium, then all you need to complete the system is to pump water from the aquarium to the main chamber and let it run back down to the aquarium from the bottom of the main chamber. This works well if your aquarium setup is not meant for display, or when aquarium is situated behind a wall with an opening for viewing, so that things above the aquarium are concealed, as they are here. Unfortunately, most of us have just a regular aquarium sitting on a wooden stand or a simple desk, so the filter has to be hidden below the aquarium. For this setup, we cannot just pump water from the aquarium to the filter because it has to get from the filter back to the aquarium somehow. Luckily, you can use an overflow system.

An overflow system is a brilliant device that lets the water flow from the aquarium as long as the level of the water in the aquarium stays above some safe level. In other words, it lets the water flow from the tank while preventing all the water draining from it. Very useful in case of pump failure or power loss.

It can either be built into your aquarium if it has pre-drilled holes in the bottom, or you can use external overflow box. Usually only people setting up saltwater systems buy tanks with holes drilled in the bottom to have continuous flow to and from the sump (so called reef-ready tanks), but you can use the same type of aquariums for a freshwater setup with a wet-dry filter. More often you would prefer to start with an external overflow box. You can buy nice ones if you do not mind spending upwards to a $100 for it. Or you can make one for about $15 yourself. There are many plans for building your own: for example, see about.com for links. I was not quite satisfied with any of these, so I made my own. Here are step-by-step instructions with photos.

A few words of caution: a home-made filter can produce more noise then an off-the-shelf unit. Most of the noise is generated in the overflow assembly and at the point where water enters the drip chamber.

If you have any questions or suggestions for me, I will be happy to hear from you. Email me: denis at gerasimov dot net. Please, put "Wet-dry" somewhere in the subject please.