New Pond Syndrome can cause problems in a new garden pond

Dear Ben,

Could you please tell me what ‘new pond syndrome’ is all about? I have heard this term before but never really understood it, and I think it’s about time I did, since I am moving my koi to a new pond very soon. Does this ‘syndrome’ occur in all ponds? Why does it happen and what exactly is it that happens? Is there anything I can do to prevent it or get rid of it?

Yours truly,

Mr Lizbo – Middlesex

Mr Lizbo,

If you are about to move your koi into a new pond (that has recently been constructed) then you really do need to know and understand New Pond Syndrome. By appreciating what can go wrong (and understanding why) with NPS then you can prepare your new pond in advance to minimise its harmful effects. But you must proceed with caution as NPS has claimed (and continues to claim) the lives of koi and other pond fish. It is also responsible for causing new koi keepers around the world a great deal of heartache, with many disillusioned beginners being inclined to give up the hobby before they’d really started. The infuriating thing about NPS and running in a new pond is that the hardest work comes at the start, and once you’ve matured your filter, pond keeping is so much easier. Unfortunately those that give up in the first few months never find this out for themselves.

What is New Pond Syndrome all about?

New Pond Syndrome is a technical way of describing what can happen if a new pond is stocked in haste. I can understand that now you have built a new pond (or if you’re lucky, had one installed for you), that you are eager to see it as you intended – well stocked with your beautiful koi. However in your rush to achieve your desired result as quickly as possible you could soon forget the basic principles of husbandry and get stung by NPS.

As soon as your new pond is stocked with koi, a continuous ‘trickle’ of ammonia will be released by them into the water. As the trickle continues, the concentration of ammonia starts to rise until the pond’s water quality deteriorates and starts to stress your koi.

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

New ponds are relatively lifeless. It will have been constructed out of inert building materials, and filled with water that has been disinfected to make it suitable for drinking, and compared to a natural water body, your new pond environment may appear to be clean, but crucially it is ‘dead’.

It is the abundance and diversity of microscopic life in a mature pond 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 the water ‘sweet’. If the population is not sufficient compared to the level of work demanded of them, then you will experience an imbalance and build up of pollutants and this in essence is New Pond Syndrome. In fact, because this toxic phenomenon is largely attributable to the filter, I prefer to call it New Filter Syndrome.

Does this syndrome occur in all ponds?

All new ponds have the potential of turning toxic if they are not stocked and run-in with care over the first few months. The larger the pond, the better the chances of a pond not experiencing extreme case of NPS – purely on the basis of dilution. But even if the diluting effects of a large pond can off-set the harsh realities of NPS, its filter will still need to mature so that when the large pond is adequately stocked, it can handle the waste produced by your koi. The maturation process will still prove to be lengthy as the different bacteria colonise, multiply and process the various forms of waste that will start to accumulate within a pond. In fact, if the levels of ammonia in a new pond are too low, then this will limit the population of bacteria that can be sustained in a filter, limiting its rate of maturation.

Why does it happen and what exactly is it that happens?

A useful way of visualising what is happening in your pond and filter is to imagine three barrels, each fitted with a tap. Barrel No.1 collects ammonia from your koi, barrel No.2 collects nitrite from Barrel No.1 and Barrel No.3 collects nitrate which is fed to it by Barrel No.2.

In a pond that is suffering from NPS, either barrels 1 + 2 (containing either ammonia or nitrite – both toxic!) will be filling up quicker than the taps allow them to empty. This will be clear by testing your water for ammonia and nitrite. The results will tell you where you are getting the bottleneck and which parts of your filtration are not coping. For example, if the ammonia is high, then the ammonia-converting bacteria will not be processing sufficient ammonia. Likewise, if you have a high nitrite, then your nitrite-converting bacteria are also in an immature state. In extreme cases, you could also get high readings for both ammonia and nitrite. However, speaking figuratively, the more mature your filter, the bigger the tap, allowing more waste to be processed. Ultimately, in a mature and balanced koi pond, the tap’s capacity in barrels 1 and 2 will be far greater than the rate at which ammonia and nitrite are produced in the system and hence ammonia and nitrite levels will always be zero. It’s the potentially deadly journey to ‘maturity’ that is what we regard as the risky part of avoiding NPS.

Is there anything I can do to prevent it from happening? And if it occurs, how do I get rid of it?

1. The most reliable method of preventing NPS is to stock your pond wisely and patiently. This will mean adding koi 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 new workload.

2. Help the maturation (open up the barrel taps) of your new pond and filter system by adding a source of bacteria. The more diverse and larger the bacterial population that your filter can sustain, the quicker they can process the waste, passing it on to the next barrel. Traditionally this has been a waiting game, waiting for Mother Nature to colonise the filters naturally (and slowly). However, filter boosters can now be added to speed up the process, or the addition of some mature filter media. You are in an ideal position to ‘donate’ some of your highly desirable mature biomedia that is virtually priceless by virtue of the breadth and diversity of bacteria it will seed your new system with. Furthermore, because it is being taken from your own pond, you can vouch for its disease status.

How do I stock the pond without risking NPS?

As soon as your new pond is stocked with koi, ammonia is released by your koi, filling up barrel No.1. As the tap is virtually closed at this stage on account of there being very little bacterial activity, the ammonia level will start to increase. You can reduce the amount of ammonia that your koi produce by stopping feeding immediately. You should also reduce the ammonia level by carrying out a partial water change with treated tap water, diluting the toxin away.

What if I get an ammonia or nitrite reading during stocking?

Even by adding some mature media from your old pond and filter, it is highly unlikely that you will be able to mature your filter and stock your pond without experiencing an ammonia or nitrite reading. Be prepared to accept low levels. However, should either rise significantly you will need to react quickly as follows:

1. Carry out a partial water change

By carrying out a partial water change, the lethal levels of ammonia (and/or nitrite) can be reduced but not removed completely, allowing the bacteria population to increase as they continue to break down the residual levels of ammonia. The nitrite peak can also be diluted, but 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.

2. Stop Feeding

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.

3. Proceed with caution

Subsequent stocking should only be continued when ammonia and nitrite levels have been at zero for a week, and then additions of new stock should be limited. For example, if you have 24 koi, stock 4 at a time. 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 required (as highlighted by your water test results).

With adequate care and attention, this initial maturing phase should take 2-3 months before you can be a little more relaxed with stocking and feeding. The test of a fully matured filter is that it will handle being overfed with no trace of ammonia or nitrite coming through into your water tests.

By understanding the science and processes behind NPS and responding accordingly, you can save yourself considerable expense on pond treatments (and at worst, replacement koi). You are in the perfect position where you can take time to run in your new pond using some of the filter maturity from your existing filter, stocking it gradually as you transfer your koi to the new pond. Best of luck!

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