koi4u-2011 facebook  koi4u-2011 hoogland
You are here: HomeGeneral ArticlesChris on KoiFlow Rates - Let The River Run

Chris on Koi

Flow Rates - Let The River Run

Just how critical are flow rates to successful koi keeping? And what about circulation, is it really necessary to move the water within a pond? There are a surprising number of common maladies koi keepers experience with their koi and water quality that can be easily remedied with a change in flow rates and circulation patterns.

Our ponds are amazingly similar to the human body. Flow rates and circulation are critical to a pond and the human body. Circulation dissolves oxygen and impurities evenly throughout the pond. Circulation in the body provides oxygen, removes carbon dioxide and metabolic waste. Fresh water from the filter is quickly dispersed throughout the pond, diluting the existing water being polluted by toxic waste and degrading organics. "Fresh" blood from the liver, kidneys and lungs (the bodies filters) is pumped to every corner of the body into each and every cell to sustain life.

A pond with a large water volume, but a limited number of koi, can have a slow turn over / flow rate. The larger volume of water is a natural buffer against rising toxic waste levels. The large volume of water (relative to stocking densities) has a reserve capacity of oxygen. However, as the fish biomass increases we have to make adjustments to maintain health and water clarity. We either have to increase the water volume or we have to increase the flow rate through the filter (preferably a larger filter).

Increasing flow rates is literally artificially increasing the water volume. More water flows through the filter at a faster rate, more molecules of water are brought into contact with the air, oxygen levels increase. The larger volume of purified, oxygenated water returns to the ponds at a faster rate. More koi can live a long, healthy life in the same volume of water.

The question must be asked - why remove ammonia quickly from the pond water? Why not let koi swim around in their own excretion and enjoy themselves. Why not have minimal turnover and leave a low level of ammonia in the water with low oxygen levels? The answers are that ammonia is toxic in minute quantities and oxygen is scarce, in water, at the best of times. A level of 0.3 ppm of ammonia is toxic to koi. Continuous lower levels are stressful to koi. 1 ppm is one ten thousandth of one percent!. Ammonia can build up rapidly within days. In some cases within hours a frighteningly high ammonia level can be registered. So it is a good idea to remove ammonia as fast as possible, hence the turnover rate.

On the other side of the coin, it is a fact that the actual ammonia level in a fully recirculating pond can never be zero - even if the filter design is so efficient as to remove 100% of the ammonia, nitrites and nitrates that passes through it. There will always be some quantity of ammonia in the pond water by virtue of the fact that the fish, and decomposing organics, are continuously adding ammonia to the water. The filter can only remove ammonia from that small portion of the pond water that is moving through it at any given time.

The ammonia that remains in the pond at any given moment is called ambient ammonia. The greater the fish load the higher the ambient ammonia level will be. Therefore, the greater the number of fish and the size of the fish in a given pond volume, the higher the turnover rate must be.

Comparing three different ponds with different stocking densities and water volumes directly with each other we will see the reasons for high flow rates and the reasons for increasing the flow rate in some circumstances. All three ponds have the same good feeding rates.

Flow rates
It is obvious that ponds "2" and "3" must have biofilters to sustain the fish population because the amount of ammonia produced each day is proportionally higher when dissolved in the pond volumes. It is also clear that although pond "3" has the largest water volume it must have, proportionally, the largest biofilter and the highest turnover rate for biofiltration as well as oxygenation. The biomass of the koi in pond "3", in proportion to the other ponds, is the largest.

If we reverse the fish stocking densities and place the three small koi from the small pond "1" into the large pond "3" the following would happen. The biomass of the koi is reduced from 25 large koi to 3 small koi. The pond carrying capacity for the limited number of fish would have massive reserves. Remember there is 10 times the water volume between the ponds. The daily ammonia production would be so diluted in the larger volume of water that it would hardly make an impact. A biofilter would not be necessary. The flow rate could be lowered substantially. A pond turnover of once or twice a day with a smaller pump would be adequate.

A larger filter and higher turnover rate would also benefit the removal of solids as larger ponds produce and attract more solids than smaller ponds. When flow rates are slow the production of organics is faster than is removed by the filter. The result - pond water will not clear no matter what type of filter you use. If the size of the filter is increased and the turnover rate is also increased, the water invariably clears.

From the point of view of solids, higher turnover rates are an integral part of maintaining clear water. Once the flow rates are correct through the filters, and the filters are correctly designed and maintained, the solids will be removed faster than with slow flow rates. The result - the water will clear.

The other major advantage of higher turnover rates is substantially increased oxygen levels throughout the system. Oxygen "activates" the entire system and is a key part of successful koi keeping.

Koi stocking densities, pond volume, filter volume and flow rates are intimately connected. Change one parameter and the others need adjusting.

Chris Neaves

Last Updated on Friday, 31 October 2008 14:29