Saltwater fish tanks in general, and reef tanks in particular require immaculate water. Pet shops occasionally have sump filters available for purchase. However, sump filters are built on a very simple idea, encouraging DIY versions.
Sump filters go by several names, including trickle filters and wet/dry filters. In a sump filter, water drains into a sump, basically a container of water. A sump contains baffles and filter media. Sump filters may also contain other aquarium equipment like heaters, protein skimmers and even other filters. This keeps them out of view. After all that filtering, the water is pumped back into the tank through a return line.
A DIY sump filter has several advantages over an off-the-counter filter. You can customize a sump filter endlessly, altering the design to your specific preferences. Depending on the filter media you select, a sump filter can provide chemical, biological and mechanical filtration. Additionally, you can hide all of your bulky aquarium equipment out of sight, under the tank in the sump. A sump filter also makes for easier water changes.
A DIY sump filter does have some disadvantages. For example, many designs require you to drill aquariums. This process is risky; it's very easy to destroy an aquarium while attempting to drill it. Additionally, if the drain-line gets clogged or vapor locked, you could cause a flood, a burned-out pump or even a fire. Setting up a DIY sump filter requires more skill than setting up an off-the-rack filter. Lastly, a sump filter can cause increased evaporation. This can in turn result in increased salinity.
Selecting your filter media is a big part of designing a sump filter. Some media encourages the growth of beneficial bacteria to provide biological filtration. Ceramic noodles, and bioballs -- spherical plastic -- can sit in a sump's various baffles to give bacteria a place to grow. You can also bag media like activated carbon to provide chemical filtration. You can also create a sump with artificial lighting to grow macro-algae, which can help filter the water. You can also hook up smaller filters into your sump to provide the three types of filtration.