Undergravel filters are back: simple filtration that works in planted tanks too

I did not expect to be excited about undergravel filters in 2026, but a recent write-up from Aquarium Co-Op made a good case for them. They were once standard in fish rooms and shops, then faded as aquascapers moved to canisters, internal filters and hang-on-backs that allow delicate aquasoil and fine sand.

The idea is simple. An uplift tube, driven by an air pump, pulls water down through gravel and over a grid of plates, so the whole floor of the tank becomes a surface for beneficial bacteria. Debris gets trapped in the gravel, and the flow is gentle, which the article says suits long-finned bettas, fry and shrimp. Maintenance is basically a normal gravel vacuum, and the plastic air stones resist clogging.

The part that surprised me was planted tanks. The author argues the old rumor that undergravel filters and plants do not mix is wrong, provided the substrate is suitable. Moving oxygenated, nutrient-rich water past the roots can help prevent root rot. The caveat is that big root feeders like Amazon swords can anchor themselves into the plates, so place them where you will not need to move them. The limit is that these filters need gravel of roughly 5 mm or larger, and cannot be used with sand, soil or other fine substrates.

For setup, you need an air pump, airline tubing and a check valve so water does not siphon out when the power fails. Plates fit together by dovetail joints, and 1 to 2 inches of gravel over the whole plate area is recommended. For a gravel-based planted tank or a big fish room, I think this is worth a second look.

Source: Aquarium Co-Op