Air lifts and your Koi pond...
What is an airlift?
Airlifts are perhaps surprisingly not a new thing. They have in fact been used in aquaculture for decades because they are ultra efficient in terms of moving large quantities of water.
They are not commonly used on Koi ponds for a number of reasons - none of which we can quite fathom out right now! We think it's because they are a bit more complicated to install. They are also a bit more complicated in working out flow rates and of course in some Koi ponds they simply cannot work because of the physical constraints of the site itself. And generally the running costs of a Koi pond are largely ignored by the pond builder - after all they are not the ones who have to pay for them once the pond has been built...
So here we present our offering on how to use airlifts and why to use them - their benefits and their drawbacks.
The basic concept of an airlift is in fact a very simple one. If you have ever seen bubbles surfacing en masse in a Koi pond, or any body of water for that matter, you will notice that the bubbles tend to break at the surface a little higher (a few millimeters) than the actual surface level of the pond itself.
The reason for this is because as the bubble rise up through the water body they 'drag' water up along with them. It is this 'viscous drag' property of water than we exploit in our air lifts.
What you do, very simply, is to force a whole bunch of air bubbles to rise up through a thin tube or pipe. As they do so the bubbles drag water up with them. The essence of the concept is illustrated below.
The general rules are as follows:
So you can see that there is a fair degree of optimisation that can take place before you get to an optimum blend of water movement vs. air flow. Then there are smaller factors such as bubble size that of course also makes a difference!
We have found that using a 63mm diameter pipe with one of our large airstones and between 20 and 30 l/min of air will give about 4000 to 5000 l/hr which is pretty good all things considered.
Airlifts thus rely on tiny head pressures, generally only a few centimeters. But this is more than enough for our Koi pond's filtration needs. If you plan your pond such that your filters are constructed on the same level ... i.e. same water level that is... and you allow sufficient large bore pipe in your filtration design there is no reason why you can not use airlifts to great success on your Koi pond.