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New Pond Syndrome

 Article published with the kind permission of Pieter de Villiers

New Pond Syndrome occurs when excessive inputs of fish waste can’t be dealt with adequately by the pond filter, leading to the build up of pollutants, which if left lingering in your pond water can be catastrophic. Such a build up of ammonia would adversely affect water quality, causing Koi a range of health problems which if left untreated could lead to their untimely death. NPS are often the first problem encountered by new Koi keepers.It can seem so extreme, with solutions seeming so long term that NPS can put people off keeping Koi all together. Many encounter it unknowingly in the form of diseased fish, (blaming the Koi dealers!) and tries medicate the problem away. Where NPS is the cause of the health problems treating, the Koi will not help.

NPS are a technical way of describing what happen if a new pond is stocked in haste.
It is understandable that having spent many hours (and money) in building a new pond that there is a great eagerness to see it as you intended - well - stocked with beautiful Koi.
In the rush to achieve the finished result in three days, we soon forget the basic principles of Koi husbandry.


Please note that, as soon as new pond is stocked with fish a continuous trickle of ammonia is released into the water. As this continues, the concentration of ammonia starts to rise until the pond’s water quality is in danger of taking a nose dive. Feeding Koi will speed up this action and the ammonia level will rise much faster!

New ponds are “relatively lifeless,” constructed out of inert materials and filled with water that has been “disinfected” to make it suitable for drinking. It is an abundance and diversity of microscopic life that processes and detoxifies ammonia ( and other pollutants) preventing them from accumulating. Any stable water body depends on a thriving population of bacteria and protozoa.If the population is not sufficient compared to the level of work demanded of them, then pollutants build up.This in essence is NEW PONDS SYNDROME


Water quality in a new pond deteriorates rapidly if the levels of inputs are way in excess of the system’s ability to handle them.There are different degrees of NPS.
Mild cases are nearly always experienced in a new system, wherever with careful stocking slight peaks in ammonia ( and a few days later nitrite) are experienced. If noted and managed these shouldn’t cause any serious health problems. However at the other extreme, real problems if not fatalities can be experienced.

Let’s say an existing pond has been emptied, and extended, and the Koi placed in a temporary pond setup elsewhere in the garden.Serious NPS could be experienced.

The temporary self-standing pond is set up with water from the original pond and installed with a new filter.
All the Koi is transferred to the temporary pond, which does not have a mature filter.
Because the filter has not been colonized with beneficial bacteria to break down the inevitable ammonia, ammonia levels will rise quickly putting the whole collection at a threat from severe stress.


Such a scenario could also be experienced after the “old” pond has been repaired or extended. Having been put into dry dock during construction, what was previously a mature filter would have been set back to its capabilities the day it was bought. Without the supply of water, ammonia and nitrite on which to exist the bacteria would be dead! Upon refilling and restocking the pond, even though the pond and part of the filter are mature, it will behave like a completely new pond system, leading to perilous peaks in ammonia and nitrite upon restocking.


Koi excretes ammonia because it is toxic.
Consequently, by excreting it into the pond water, the whole pond environment inevitably turns toxic (unless it is broken down at the same rate by bacteria)
Typical ammonia intoxication symptoms are gasping at the pond’s surface, lethargic behavior and excess mucus secretion. If your fish manage to survive the stage in ammonia, they will also have to overcome the associated nitrite peak. Nitrite behaves differently from ammonia in several ways.
Firstly compared to ammonia, nitrite is far more persistent. Although ammonia levels may have dropped quite rapidly once the Nitrosomonas bacteria have kicked in, it takes Nitrobacter much longer to process nitrite.
In extreme cases nitrite levels can accumulate - to such high concentrations - that they even inhabit the beneficial action of those bacteria that break it down. An accumulation of nitrite in the pond causes nitrite to accumulate in your fishes’ blood as they indiscriminately absorb through their gills. This reduces the oxygen-carrying capacity of their blood, causing Koi to gasp, flask or scratch through irritation.



Gil damage:-

1.Decreased blood O2 and/or ...
2.Interrupted osmoregulation
Increased internal ammonia:-
1.Liver and brain damage.
2.Internal acid-base imbalance
3.Increased disease susceptibility.

Blood hemoglobin oxidizes into met-hemoglobin:-

1.Blood incapable of transporting oxygen.
2.Increased disease susceptibility

Gill and skin damage:-

1.Increased acidosis of environment.
2.Concurrent increase in non-related toxic substances.
3.Increased disease susceptibility


The ammonia-to nitrite seems to be established first; hence, the nitrite spike.
The lethal level of ammonia can be partially removed with a partial water change. This allows the bacteria population to increase as they break down the residual levels of ammonia.
The nitrite level will also be diluted to a safe limit by partial water changes, although by adding salt ( 3kg/1000lt) would help against the nitrite sting.
Salt “protects” against nitrite poisoning. It does it by competing against the nitrite for ion transfer across the gills. If you have lots of chloride ions in the water, it goes into the fish in greater numbers then the nitrite.


Salt is fine to protect the fish against nitrite and shouldn’t inhibit the startup of the filter system.
As ammonia excretion is related to the level of protein in the diet, Koi should not be fed while there is a positive ammonia reading.
In addition, should the first partial water change did not reduce ammonia levels below acceptable levels, then a further water chance would be necessary.
Subsequent stocking should only be continued when ammonia and nitrite levels have been at zero for a week, and even then additions of new stock should be limited to about 30% of the existing stock. For example, if you have 15 Koi, stock five additional fish at most.
Continue to test for ammonia and nitrite and ensure that the filter manages to handle the increased stock, intervening with water changes and reduction in food if necessary.


If the pond was “constructed” with material that will increase the pH levels no fish should be added if the pH reading is above 9.
A pH reading above 7 is an alkaline condition, although a Koi pond must have a pH level of between 7 and 9, and ideally a level between 7,5 and 8,5.
Excessively alkaline water likely to have been cause by a pollutant - cement or builder’s lime is a prime suspect - regarding a “new” pond.
The symptoms of an excessively alkaline pond will cause Koi to secrete a slimy mucus film, and may show signs of gill and fin damage.
Lowering the pH ( with no fish in the pond) various acids like Orthophosphoric Acid and Hydrochloric Acid can be used for a fast solution. Small quantities must be added very gradually over a period of a few days, with regular pH level testing.
If the pH seems to be between 7,5 and 8,5, run the pond for another seven days, only after which Koi should be added to a safe pH level pond.
Should the pH be acidity, lower then 6, soda ash could be used to raise the pH before any fish is added to the pond. This normally occurs then one fills the pond with borehole water.
Oyster shells are good stabilizers of pH.


So when building a New pond, reconstructing, repair or restart an old one.....Beware of NPS!

Now see the article on Bioseeding a new filter

Last Updated on Monday, 19 April 2010 16:28