How to Build a Koi Pond - Turnover Rates

Critical success factor this...

The rate at which your total pond volume is circulated through your Koi pond filter system is called the turnover rate. It is an important number but is based on rules of thumb and can very substantially from pond to pond...

Building a Koi pond - Turnover rates

Turnover rates are most important when considering your bio filter section of the filter chain. In considering this one need to be aware that a filter chamber has a finite capacity, and the flow rate of water will determine the residence time of the pond water in this chamber.

The residence time is thus the maximum time that the pond water can be in contact with the bio media. So if a filter chamber has a residence time of two minutes, the biofilm and the active bacteria have two minutes to strip out all the ammonia and convert that to nitrites and then to strip out all these nitrites as well.

Many theories abound about how the nitrosomonas and nitrobacter go about their invaluable work. It is argued that the reaction time of ammonia to nitrite abd nitrite to nitrate is in fact almost instantaneous when the bacterium involved decides to 'get on with it'.

However, what is less well understood is the actual reaction cycle depending on concentration. If you have a very dense bio media with an active healthy biofilm, it is possible that a two minute contact time would be perfectly adequate.

However, there is no evidence that I have yet to come across anyway, that contests one can have too MUCH contact time with the biofilm. So, as with most things in Koi pond filtration, more is better.

That said, don't fixate on trying to get maximum contact time by reducing the flow rates through the system. If a Koi pond is turned over too slowly, after a good munching on good quality Koi pellets, the 26 85cm Koi in a 10 000l Koi pond are literally going to cause an 'ammonia speed wobble' - and the results can be quite disastrous. It is rare, but a bio filter can go into ammonia shock - a condition in which the ammonia overload is too intense too quickly and bang, problems start to manifest.

If your filter does not strip all the ammonia out in it's first pass, with a reasonable turnover rate it at least has the chance to try again two or so hours later...

New filter systems can be very temperamental to get going. They can take some time to 'take' and start growing masses of bio film. During these startup's leave well alone. Feed your Koi a minimum, measure your basic water quality parameters regularly (ammonia, nitrite & to a lesser extent nitrate). Let the pond find it's own equilibrium - and this can take quite some time. It is however, best left to nature.

You can of course cheat and help jump start the process with Bao Bio Clear which helps to reduce the time taken for the bio media to develop bio film growth.