18 March 2017

Tony Roocroft
Water fish ponds, air pumps & oxygen

The following comments are really aimed at koi fish keepers rather than the casual garden water ponds enthusiast.  Nevertheless the points made are just as valid for small water ponds as well as
large water ponds. Based upon my experience few small water ponds actually use air pumps, neither do these water ponds need them.  The reason is that the demands for oxygen by both the fish and biofilter bacteria are less urgent.

Ponds, fish and oxygen ... the best kept secret in koi fish keeping

Before talking a little about air pumps themselves lets discuss the critical need for oxygen in water ponds in a bit of detail.

We survive on this earth because we can breathe oxygen.  Oxygen drives the human body. It is the same with most other life on this planet.  Koi fish need it and the bacteria that keep the water ponds clean need it.

It is probably fairly obvious why water ponds containing fish need oxygen but less obvious why the biofilter process needs it ... and in fact needs it in large quantities especially when fish are fed.

Ponds ... before feeding fish

If you imagined that you had an analyzer attached to the water ponds circulating pump system measuring oxygen and ammonia just before the biofilter and also just after the biofilter this is the kind of thing you would see on your results .... take this as a basic explanation and not the gospel truth.

Just before feeding the fish ammonia levels and oxygen levels at the water inlet side of the biofilter would be low and high respectively.
Now assuming the biofilter is working efficiently the outlet water side would show the ammonia level would be zero and the oxygen level would be a bit lower than on the inlet side of the biofilter.

The reason for this is that the biofilter bacteria controlling water purity in the pond's system need food (the ammonia) and oxygen to convert the food to useful energy and waste products (nitrite and nitrate).  Water ponds in good health achieve this result without your even knowing what is happening and your fish do not become stressed owing to high ammonia levels.  Plants for water ponds also help in the process.  Lets take a look what happens just after you feed your fish. 

Water ponds ... after feeding fish

All fish food contains nitrogen which when it passes through the fish's system is converted to ammonia. This happens very quickly. So if you repeat the measurements above for water ponds under feeding circumstances this is what you would see ...

At the inlet to the biofilter a much higher ammonia level with a normal high oxygen level would be observed. On the outlet side of the biofilter you would see a much lower oxygen measurement and a
significantly lower ammonia level.

What has happened in the water ponds system? .... the bacteria consumed as much of the ammonia as possible and absorbed lots of oxygen from the circulating water to be able to achieve this. However they could not remove all the ammonia in a single pass through the biofilter because the oxygen level was depleted too much too quickly.

For the bacteria to be able to do better at removing the remaining ammonia next time around the oxygen removed has to be replaced .... this is achieved in many ways such as using a waterfall, using a sprinkling or foam fountain effect, the action of wind on the water surface and of course by using air pumps. If you did not replace the oxygen removed then eventually the bacteria would die in large numbers and thus would not be able to convert ammonia. Your fish would also die in time as the levels of nitrogen based poisons built up.

This is why a water ponds pump must run 24 hrs per day in fish ponds.

Air pumps and how to use them in water ponds systems

Based on the above discussion it is obvious that biofilter bacteria need lots of oxygen and that oxygen is removed in the biofilter continuously in the biofilter process itself. Question then .... where is the best place in any water ponds system to add air or oxygen?

Correct answer .... directly into the biofilter system as close a possible to where the bacteria are sitting. This is why vortex filters and Japanese matting work so fantastically well together in any serious water ponds system ....but only by pumping copious volumes of air around the Japanese matting matrix.

It is also the reason why fluidized bed filters are better than box filters but not as good as vortex filters unless air pumps are used ... then they should be as good as vortex filters with Japanese matting.

So it is not the Japanese matting itself that is the secret to excellent biofiltration it is the fact that this medium lends itself to efficient contact between bacteria, food source and oxygen.

Conclusion to be applied ... all water ponds

Add as much air to water ponds as you can using air pumps and air stones to distribute the air if necessary (highly recommended for koi ponds and gold fish ponds that are heavily stocked). You can add the air directly to the pond, the filter, the waterfall and anywhere else you can think of.

A further conclusion from the above is .... feed fish small amounts often rather than a large amount at once to allow the biofilter to work efficiently.