Nitrite and ammonia pond problems – New Filter Syndrome.

I wrote to you last month with a query relating to murky water in my newly constructed pond. In your reply, you asked me to test for ammonia and nitrite as you suspected my water quality might be having an impact on the health and behaviour of my koi. Unfortunately I can now confirm that my ammonia is at 0.1ppm and my nitrite is at 30ppm – both too high.

Since they stopped feeding, I have had a problem with fin rot, and I just can’t get the ammonia or nitrite levels down to zero. This is really upsetting me he and my wife as since stocking our pond with koi three to four months ago, we have only really had success in the first month, please help.

A: Thank you for getting back in touch so quickly with further details. Your case is now a lot clearer, and your positive ammonia and nitrite readings confirm that your pond is suffering from being stocked too quickly. All of the symptoms that you have described are common and attributable to an accumulation of toxic by-products excreted by your koi. The encouraging aspects of your current situation are having identified the cause, it is relatively straightforward to rectify and once rectified will lead to immediate improvements in the appetites and health status of your koi.

However, before reading on, do the following immediately:

1. Stop Feeding

2. Aerate vigorously from the bottom of the pond

3. Carry out a 30% water change with treated water.

The what’s going on in your pond?

The vast majority of ponds (and aquaria) will experience to some degree the phenomenon that your pond is experiencing at the moment. Your situation sounds more extreme than most. The phenomenon of new pond accumulating toxic waste has been described as New Pond Syndrome. Perhaps a more accurate description would be New Filter Syndrome as your pond water has deteriorated as a result of your filter not being sufficiently mature to process the waste that your koi are producing.

What causes new filter syndrome?

The new a multi-chambered filter that you recently installed will contain media for both mechanical and biological action. The mechanical chambers will remove or trap suspended particulate matter and will be effective immediately. Your biological chambers however are missing the vital ingredient – beneficial bacteria. These bacteria are the life that give your chambers their biological action, breaking down the waste. The more mature and diverse the population of bacteria in your filter, the better they will process the waste. Different bacteria process different types of waste, passing semi-processed waste down the line for other bacteria to process further. The rate at which your pond can handle fish waste is therefore determined by the density and diversity of bacteria in your filter.

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 (see Figure 1).

At present barrels No.1 and No.2 in your pond appear to be filling up quicker than the taps will allow them to empty. However 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 one and two 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.

Solving NFS:

Looking at Figure 1, it clearly shows two ways that you can get on top of your pond’s problem.

Stop the barrel from filling up as quickly

Open the taps to empty the barrels as quickly as possible.

Stop the barrel from filling up as quickly.

As soon as an new pond is stocked with koi, a continuous trickle of ammonia is released into the water. As the tap is virtually closed at this stage on account of there being very little bacterial activity, the ammonia barrel will start to fill up. 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. However you must be in a position to start feeding them again soon, so you need to look at a way of opening up the taps so your filter can handle all of the ammonia that it receives.

2. Open up the taps. Bacteria are your only solution to opening up of the taps. 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 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 (or filter extract) from a fellow koi keeper whose pond you trust has been free from problems and disease.

What happens now?

You will soon know whether your partial water changes have started to take effect by testing your pond water for ammonia and nitrite. You’re aiming for ammonia and nitrite levels to be zero. If having retested your water, the levels have dropped considerably then wait for another couple of days to give your bacteria the opportunity to breakdown the remainder, enabling the bacterial population to grow. If how ever, after several water changes your ammonia or nitrite levels are still dangerously high, you will need to carry out further water changes.

Nitrite levels in particular are more persistent compared to ammonia as bacteria appear to find it more difficult to break them down into nitrates. Only when you have stabilised your ammonia and nitrite levels at zero or close to zero should you start to think about feeding your fish again. Your koi will easily last two weeks without food (and if they are suffering from ammonia or nitrite toxicity, their appetites will be much reduced anyway).

Once you do recommence feeding, continue to test for ammonia and nitrite (being aware that these may well lag two to seven days behind the first feeding). If you get a positive ammonia or nitrite reading then cease feeding and dilute with a partial water change again.

NFS and your koi.

Your letter mentions that your koi are now suffering from fin rot. Under the circumstances, this is not surprising. Fish excrete ammonia because it is toxic. Consequently, by excreting ammonia into the pond water, the whole pond environment inevitably turns toxic (unless it is broken down at the same rate by bacteria). Typical initial ammonia intoxication symptoms are gasping at the surface, lethargic behaviour, and excess mucus secretion. An accumulation of nitrite in the pond causes nitrite levels to rise in your koi’s 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. Over prolonged periods of stress, your koi will become more susceptible to disease, and this has clearly happened in your pond.

In order to help cure koi through this stressful period, in addition to carrying out the water changes, supply your pond with additional, vigorous aeration, diffused from the pond bottom. This will support your koi’s oxygen debt as they struggle to carry oxygen around their body.

Having restored your koi to satisfactory water conditions, you should treat your pond with a course of broad-spectrum anti-bacterial treatment to clear up any fin rot problems. Also, continue to monitor closely the health of your koi over the next few weeks as they will have become very susceptible to other diseases. Continue to verify that the ammonia and nitrite levels remain at zero.

Over time your filter will mature steadily so that it can handle waste in increasing amounts, allowing you to stock your pond toward its limit. Fortunately, a pond and filter system only has to go through this teething process once, and once it has matured, your filter will support your koi for many more years to come.

New filter syndrome is the biggest threat to koi in any new pond’s early period and unfortunately we experience it when we have little experience of koi keeping. But we also have an idyllic image in our minds of how we want our koi pond to look, hoping to achieve the finished result in record time. Hopefully this time, NFS is not the winner and your pond will go on to support your koi for many trouble free years to come.

Kill blanketweed and string algae.