Pond Air Pumps
Pond air pumps are a very useful if not vital piece of kit to increase aeration for your koi. You may not need one running continuously but an air pump can be kept for backup in such cases as on hot days when the oxygen levels can plummet. They are also useful for treatment bowls and quarantine tanks where medications can lower the waters ability to absorb oxygen. You should try to keep the water in a koi pond as close to saturation point with oxygen, and aeration helps to degas CO2 and Ammonia. There are test kits and meters available if you are not sure but a general rule is if you can't hear the water movement you need more. This doesn't mean your koi pond has to resemble a jacuzzi but a pond air pump can provide extra air with airstones placed in the filter chambers.
There are many very good pond air pumps available on the market and their quality is reflected in their price. If the pump is going to be running continuously as part of the life support system for your koi then it probably pays not to scrimp as reliability and air output are important. Some of the latest air pumps are piston driven so there's no rubber diaphram to wear out. When looking to buy a pond air pump you need to check how many litres of air it produces and also at what depth. It's no good buying an air pump that supplies 40 litres at 2ft but won't pump through an airstone that's at the bottom of your 6ft pond! Also worth baring in mind is the wattages can vary between makes which can add up making a difference to your electricity bill.
Recently I needed to buy a new pond air pump for my quarantine tank. Considering all the options I eventually bought the SuperFish Koi-flow 20 pictured above. This is a make I have never heard of before and to be honest it probably isn't the best but there's no denying it's good value. At £49, less than half the price of others it may not have a fancy brass distributor but it comes with 6 airstones and plenty of airline. The build quality is quite good too with a metal body and it's very quiet. 20 litres of air is enough for a small pond and there are larger models but at that price you could get several and at 15 watts they should be cheap to run. The only complaint I would make is the power cord is a bit short but positioning it close to a power supply above the pond level it not too much trouble. I'll update how it gets on.