Modular undergravel filter

This undergravel aquarium filter consists of several modular parts, allowing you to adjust its total surface area to fit different aquarium sizes. The smallest possible configuration measures 26×15×4.5 cm.

The filter is made up of a main module, which features three holes where a hose connector can be installed. The outlet can be directed to the side, the back wall (through an opening in the aquarium), or vertically upward inside the tank. The connector screws into one of the holes and is secured with a mounting nut; the remaining holes can be closed with sealing caps.

Additional extension modules can be added to increase the length of the filter, and the setup is completed with an end module. For small aquariums, the end module can be connected directly to the main one.

Unlike standard flat undergravel filters, this design features a pyramidal shape, which increases the contact surface with the substrate on the same footprint. The angled sides help to visually hide the filter when placed near the aquarium wall—except for the main module, which should be close to the wall when the outlet goes through it.

I'm a big fan of soil filters and I've made a few of them. It’s not recommended to plant directly above the undergravel filter. Plant roots tend to grow through the structure and may clog it over time. However, the filter does not have to cover the entire bottom of the tank – depending on the configuration, it forms a strip only 15 cm wide. You can use one or two rows; plate 5 in the print project contains the connector for attaching the second row. This allows you to place it along the side or in the foreground of the aquarium, where plants are not intended.