Which air pump to use for your Koi pond...

Not all pumps are created equal...

Nigel Caddock NI

How do start...

And so then along came Secoh and manufactured a great 40 l/min air pump. The problem was their bigger models never met the same performance of the 40s and specifically, in common with numerous makes, the diaphragms emitted dust which blocked air stones and even multi port outlets. This in turn can increase back pressure and precipitated premature failure by default.

Add to this a disturbing propensity for air pump makers to specify operating depths that effectively made them inappropriate for Koi ponds. It never did stop them selling them to Koi keepers though, as we pointed out. Nevertheless very disappointing. Since the mid 1990s many manufacturers have emerged and delivered a wide range of air pumps in a wide price disparity, so how do you choose which air pump to buy?

Performance data can also be useful but make sure you are comparing like with like. Manufacturers are masters at presenting technical data that makes and shows their products in the best possible light, for example Sequence show flow rates for their circulating pumps without catch baskets (leaf traps). That's fine as long as the pump you are comparing with does the same. Its all no real problem with that as long as the playing field is flat or at least flatish!! In an effort to clarify this we have some numbers for you to consider.

Performance curves in relation to air and water pump performance are standard tools of the trade to most professionals, for we hobbyists they are normally just utterly confusing. In an effort to blow the gaff on this mystique we thought we would present to you one and discuss it in detail. There is no doubt that by far the most popular size of air pump is still the 40 litre per minute unit. But what does the date really mean to us as Koi Keepers and how can this information help us make a good air pump buy decision?

First its important to consider that there are several key elements that contribute to the performance of an air pump.

1/ Output expressed in litres of air per minute

2/ Pressure usually expressed in kg/cm2.

3/ The other key factor is amount of power used.

The problem is these terms mean little to most Koi people so we thought we would try and help make it more understandable. The pressure and power numbers are however equally compelling, and in this regard not all air pumps are equal, in fact the devil is always in the detail so check the performance curves. For example its not much use in deploying a 40lpm unit to drive the air domes in your 2 metre pond when because of your chosen units inability to cope with pressure (pond depth) it actually dribbles a pathetic 10 lpm at 2m! This is where paying attention to the performance curves of air pumps and water pumps is vital.

The profile of these curves are also vital when selecting which unit is best for you, and its important to appreciate that this can be different for each individual application within your system. For example the only application in most systems that really demands performance even at 1.8m are turbo drains. For filter aeration where a maximum operating depth is approx 3 and at 3 a TP50 will deliver approx 60 litres of air per minute.

Ensuring you get the right unit for your application this is another reason for you to invest a little time understanding how the curves work and how to interpret them, and it can save you a lot because if you deploy a unit incorrectly chances are it wont perform as you hope and it may even compromise its performance and shorten its operational life. 

There is another useful rule of thumb that relates to power consumption. In general a good performing air pump will deliver 1 lpm for 0.8watt.