New Pond Syndrome. How to successfully run in an mature a new garden pond.

Irrespective of whether you subscribe to global warming as the cause of the recent Noah-proportion floods, there is no escaping the fact that they have happened on a scale and frequency barely experienced before.

Flooding and NPS?

The recent flooding provides us with a vivid illustration of what happens when a pond experiences new pond syndrome. Throughout 2000, months of incessant rain turned even the slowest of brooks, ditches and streams into torrents, brimming with their load on its way down to the valley, which was already running at full capacity. As the main rivers could not handle the incessant supply of water from the hills, the levels kept on rising, until the banks burst. This is a parallel to the series of events leading to New Pond Syndrome, where excessive inputs (this time, fish waste) cannot be handled adequately by the filter, leading to a build up of pollutants which if left could 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 ultimately lead to the death of koi.

What causes NPS?
New Pond Syndrome is a technical way of describing what can happen if a new pond is stocked in haste. It is understandable that having spent hundreds of hours (and pounds) in building a new pond (or if you’re lucky, having one installed for you), that there is a great eagerness to see it as you intended – well stocked with beautiful koi, thriving in you pond. In the rush to achieve the finished result in 3 days, (well if changing rooms can do it….) we could soon forget the basic principles of husbandry as we are carried away with our emotions.

As soon as a new pond is stocked with fish, a continuous ‘trickle’ of ammonia is released into the water. As the trickle continues, the concentration of ammonia starts to rise until the pond’s water quality is in danger of ‘bursting its banks’.

This doesn’t happen in most other ponds, so why does it happen in new ones?

New ponds are relatively lifeless. Constructed out of inert materials, and filled with water that has been disinfected to make it suitable for drinking, compared to a natural water body, a new pond environment is dead.

Unfortunately, it is the abundance and diversity of microscopic life that processes and detoxifies ammonia (and other pollutants), preventing them from accumulating. Any stable water body (whether natural or artificial) depends on a thriving population of bacteria and protozoa to keep them ‘sweet’. If the population is not sufficient compared to the level of work demanded of them, then we experience an imbalance and build up of pollutants and this in essence is New Pond Syndrome.

What can make it worse?
In the same way a river is caused to flood, new pond syndrome deteriorates rapidly if the levels of inputs are way in excess of the system’s ability to handle them. For instance, there are different degrees of NPS. Mild cases are nearly always experienced in a new system, where even with careful stocking, slight peaks in ammonia and then a few days later in nitrite are experienced. If noted and managed so as not to reach lethal levels for any period of time, then even though NPS has occurred, there should not be any serious health implications. However, at the other extreme, real problems, if not fatalities can be experienced.

Lets say an existing pond has been emptied, and extended, and the koi placed in a temporary pond set up elsewhere in the garden. Serious NPS could be experienced at 2 stages:

1. The temporary self-standing pond is set up with water from the original pond and installed with a new filter. The full complement of stock is transferred en-masse to the new pond which does not have a mature filter. As the filter has not been colonised with beneficial bacteria to breakdown the inevitable ammonia, then ammonia levels will rise quickly (on account of the relatively high stocking density) putting the whole stock at threat from severe stress.

2. Such a scenario could also be experienced after the new pond has been extended. Having been put into dry dock during construction, what was previously a mature filter, capable of handling even the heaviest feeding and stocking rates would have been set back to the day it was bought. Without the supply of water, ammonia and nitrite on which to exist, the bacteria would have died, setting the filter back years. Upon refilling and restocking the newly extended pond, even though 1/3 of the pond and part of the filter are mature, they will behave like a completely new pond and filter, leading to perilous peaks in ammonia and nitrite upon restocking.

How does New Pond Syndrome affect koi?
Fish excrete 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 surface, lethargic behaviour, and excess mucus secretion. If fish have managed to survive the surge in ammonia, then 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 having built up in a new pond. Where ammonia levels may have dropped quite rapidly once Nitrosomonas bacteria had kicked in, with nitrite, it takes Nitrobacter much longer to process this stubborn pollutant. In extreme cases, nitrite levels can accumulate to such high concentrations that they even inhibit the beneficial action of those bacteria that break it down. An accumulation of nitrite in the pond causes nitrite to accumulate in their blood as they indiscriminately absorb through their gills. This reduces the oxygen carrying capacity of their blood, causing koi to gasp, flash or scratch through irritation.

Confirming New Pond Syndrome
NPS can be confirmed using test kits. Ammonia and nitrite test kits will soon highlight the problem by registering high levels. Having confirmed a problem caused by your immature filter, continue to test and observe the ammonia peak and fall, followed by the nitrite levels peaking and falling as it is processed by the filter. This is the period through which your filter really starts to mature (Figure 1).

How to respond
Figure 2 shows how remedial action can reduce the problem so that koi stress is kept to a minimum, and the filter is still encouraged to mature. By carrying out a partial water change, the lethal level of ammonia can be removed, but not removed completely, allowing the bacteria population to increase as they break down the residual levels of ammonia. The nitrite peak can also be diluted, again, not totally removed so as to deny the bacteria a chance to mature, but at the same time to a safe limit for the fish.

As ammonia excretion is related to the level of protein in the diet, fish should not be fed while there is a positive ammonia reading. In addition, should the first partial water change not reduce ammonia levels below acceptable levels, then a further water change would be necessary.

Subsequent stocking should only be continued when ammonia and nitrite levels have been at zero for a week, and then additions of new stock limited to 30% of existing stock. For example, if you have 12 koi, stock 4 additional ones at the 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.

Preventing New Pond Syndrome
1. The most reliable method of preventing NPS is to stock your pond wisely and patiently (Figure 3). This will mean adding fish only a couple at a time, monitoring ammonia and nitrite levels, observing and recording levels so you can satisfy yourself that the filter is coping with its workload.
2. Help the maturation of your new pond and filter system by adding a source of bacteria. This can be either in the form of a proprietary preparation, or obtaining some mature media (or filter extract) from a fellow koi keeper. This will provide your filter with high levels of ammonia and nitrite loving bacteria straight away, rather than waiting for them to arrive naturally.

3. If you are undertaking pond alterations or needing to house koi in a temporary pond, prepare it well in advance to introducing koi. This will mean taking some of the existing media from the original pond and using it to provide your temporary pond with ‘instant maturity’. Likewise, when returning your fish to your new and improved pond, transfer the fish gradually, over a matter of weeks, keep feeding to a minimum and use some of the media from the temporary pond to seed the new filter. Continue to monitor water quality and respond accordingly.

New Pond Syndrome is often the first (and most expensive) problem encountered by new fish keepers. In some cases, it can seem so extreme or final with solutions seeming so long term, that NPS can put people off keeping koi altogether. Many first encounter it unknowingly in the form of diseased fish appearing, hoping to medicate the problem away. In fact where NPS is the cause of health problems, treating fish will not solve the problem. By understanding the science behind NPS and responding to it, we can save ourselves considerable expense on pond treatments and at worst, replacement fish. NPS can be serious, but it needn’t be.