Complete pond aerator EHEIM AIR 500 or AIR 1000

The unit delivers air through two 5 m pipes, each with its own diffuser and its two-in-one fitting. Spread the two diffusers so that they cover both halves of the pond rather than grouping them together, since a single column of bubbles draws water up from the bottom over only a small area, whereas two well-placed columns stir the whole pond. Place them slightly above the bottom rather than directly on the sludge, otherwise every start-up will stir your sediment back into suspension: a flat brick, a tile or a weighted basket slipped under each stone is enough to hold it a few centimetres above the deposit. The fineness of the bubbles depends on the diffuser and not on the pump, and fine bubbles offer more surface area for exchange with the water than a coarse boil, while making less noise. Finally, review the position of the diffusers after a few days, watching where the water is actually moving.

Warm water holds less dissolved oxygen than cold water, and summer is precisely when your fish consume the most and the organic load is at its highest. Aeration matters most towards the end of the night, when plants no longer produce oxygen while fish, bacteria and plants all carry on respiring. Dissolved oxygen therefore reaches its lowest level just before dawn, and that is when fish losses most often occur. In an aquaponic circuit, oxygen serves the fish, the biofilter bacteria and the roots alike, and aeration separate from the circulation pump keeps a margin in hand when the fish load increases. The article on summer maintenance covers what changes as the water warms up.

In winter, aeration meets a different need. A column of bubbles keeps one spot free of ice, which lets decomposition gases escape instead of building up beneath a sealed surface, and it is this build-up that causes winter losses in a pond covered with ice for several weeks. Raise the diffusers to mid-depth rather than leaving them on the bottom, because the aim is to keep a hole open, and full mixing would carry cold surface water down into the deep zone where your fish overwinter. This deep zone is in fact the mildest part of the pond throughout the winter, and it is the one you must avoid stirring up. The guide to building a system at home returns to the place of aeration in a complete circuit.

Power consumption and noise both matter in everyday use. At 5 or 8.5 watts, this aerator runs continuously for an annual consumption of around 44 or 74 kWh, so there is no reason to switch it off at night, which is precisely when it is needed most. The noise comes less from the motor than from vibration passed on to whatever it stands on, so a foam mat or a simple board resting on rubber solves the problem. Avoid hollow supports and sheet metal, which act as a sounding board, and choose a slab or a solid low wall if you have the option. Finally, think about shelter: the casing is not designed to be left out in the rain, and a ventilated box, a niche in the pond edging or a simple canopy will do, provided air can circulate around the air intake.