Sump filters, also known as wet-dry filters or trickle filters, are renown for their biological filtration. And unlike most aquarium filters, most people assemble them on their own rather than purchasing a pre-made filter. This allows people to design a filter to meet their specific needs and tank size. Unfortunately, a DIY filter does not come with instructions or a warranty, which daunts some. However, with a little research and a DIY spirit, it is possible to construct such a filter.
Check your sump for leaks. The best way to do this is to fill the sump with water, mark the water level in marker and wait two days. If the water level is still at the mark, there is no leak.
Install any baffles to your sump. Baffles are square plates of glass or acrylic that direct water flow in the sump. Just glue them in place with aquarium silicone. Allow the glue two days to cure before getting it wet.
Install the overflow box and return spigot. Most models simply hang on the aquarium. Position them on opposite sides of the back of the tank.
Run vinyl tubing from the return pump in the sump to the return spigot, and from the overflow box to the "in" side of the sump. In most spigots, pumps and overflow boxes, the tubing just slides over a nozzle.
Add any filter media to the sump. This may include carbon, ceramic noodles, bioballs or zeolite. Only use zeolite in freshwater.
Install any secondary filters, skimmers, heaters or pumps in your sump. One of the fringe benefits of a sump filter is that you can hide your life-support equipment in the sump.
Fill the sump and any secondary pumps or filters. Then, activate the return pump. Once the water starts returning to the sump from the overflow, mark the level with a marker and remember to never fill the sump above that level when the pump is running.
Get a return pump that can handle at least five times your tank volume per hour (your tank volume x 5 = gallons per hour). Always prime pumps. Most pumps will not work if you don't fill them with water first.
Be sure and leak test anything that holds water. Use caution when working with water and electronics.