You can never have too much air in a Koi pond, it is necessary for the fish and the filter bacteria to thrive. Koi need more oxygen than other ornamental fish, and also produce far more waste.

The fishes' waste must decompose into harmless substances, so the beneficial filter bacteria need as much oxygen as possible to process this waste. In fact, it's been calculated that 90 per cent of the oxygen content of pond water is used by these bacteria, so you can see why Koi keepers have to be constantly replenishing their systems.

In addition to their aerating properties, venturis circulate water in the pond, providing a gentle current for Koi to exercise against. Venturis also direct sunken debris to one area.