The Paffrath bowl is also known as the Paffrath trough and is named after its inventor, Kurt Paffrath, a renowned author of aquarium literature. This simple device is used in freshwater aquaristics to dissolve carbon dioxide (CO₂) in water. Carbon is an essential nutrient for aquatic plants and at the same time influences the pH of the aquarium water. In aquaristics, this nutrient element is usually supplied via a CO₂ system.

Design of the Paffrath bowl

This simple CO₂ dosing device consists of an inverted bowl or trough that is attached, for example with suction cups, just below the water surface in the aquarium. The upward-facing base of the bowl usually has one or two openings. One of them is used for supplying CO₂. Here the Paffrath bowl is connected to a CO₂ system with 4/6 tubing. Since no particularly high working pressure is needed for this, the Paffrath trough is suitable for both refillable and bio CO₂. The second opening, optionally equipped with a short piece of tubing and a shut-off valve, is used as a false-gas vent to let air, which is lighter than CO₂, escape from the bowl.

How the Paffrath bowl works

The gas fed in from the CO₂ system collects under the bowl and forms a larger gas bubble. At the boundary between this CO₂ bubble and the aquarium water, the gas diffuses into the liquid. By choosing bowls of different sizes, the size of the contact and diffusion area can be varied, so the amount of CO₂ to be dissolved can be adapted to the size of the aquarium. The efficiency of CO₂ dissolution can be increased considerably if water flow, for example from the outlet of an external filter or a separate water pump, hits the contact area intensively.

Advantages of a Paffrath bowl

The advantages of a Paffrath trough lie in its simple principle, so you can quite easily build one yourself. Purchase costs and materials are correspondingly low. Unlike diffusers, for example, the Paffrath bowl does not need a high working pressure. This dosing device is therefore especially well suited for bio CO₂. The bowl is also almost silent, apart from the occasional pops of the false-gas vent. The Paffrath bowl is a suitable dosing device especially for small aquariums, so-called nano tanks.

The ADA Mini NA set also relies on the principle of a Paffrath bowl.

Disadvantages of a Paffrath bowl

Visually, the Paffrath bowl is not a particularly decorative piece of equipment. In larger aquariums, the bowls also have to get bigger and bigger, and therefore become more distracting to the viewer's eye. When it comes to CO₂ solubility, the Paffrath bowl reaches its limits. Diffusers, for example, are much more efficient here, since they atomize the bubbles into smaller bubbles. However, more pressure is needed for that.