New Pond Problems in a small pond.

Dear Ben,

I have got a little pond, only 5ft x 4ft, and 18in deep, I have six little koi (5in long) and eight little orfe (2in long maximum). My pond has a filter pump going through a UV clarifier and into a box filter, it is quite a new pond about two months old.

My problem is the water quality is not good, I have done numerous things to rectify it, and as I’m new to koi keeping I’m very keen to get it right.

The pH is 8.5 the ammonia is steady at 1.2mg the nitrite is 1.0mg and the nitrate is 50-100mg. I have turned off the UV to give the bacteria in the filter time to mature and have steadily added more bacteria to the filter to help the nitrite levels reduce, I may have over fed the fish a bit at first, but I have now reduced feeding down to next to nothing for the last week.

I have added some pond salt to help and have been adding Ammonia Away, this does reduce the level temporary but it rises again slowly. The pond is made of Railway sleepers with a pond liner inside and the fish seem happy enough. My neighbour who has koi says I’m worrying too much, but I know with my limited knowledge that the levels should not be this high. I have done a partial water change down to six inches from the bottom, are the bacteria being affected by the Ammonia Away, and salt, and water changes?

Never mind being addicted to koi, I’m now addicted to testing the water! Can you help as I would like to get the water right before it starts to affect my new little friends.

Welcome to the world of koi keeping – and the obligatory steep learning curve!

Thanks for your email which is full of very helpful detail. Your experiences are not uncommon amongst koi keepers as all of us have had to tread carefully through the first few months as our pond and filter matures to support a balanced, healthy stock of fish. There are recommended ways of accomplishing a mature pond without encountering too many water quality problems, but from your description, it sounds as though you might have made a number of unfortunate errors that are only now starting to cause you some problems. Furthermore, your pond is so small (<200 gallons by my calculation) that any factors that adversely affect your water quality will be amplified throughout the pond as opposed to being diluted away if you had a larger pond. In order to make sense of your current experiences, and to pot a positive way ahead, you need to answer 3 questions:

What is actually going on in my pond to cause the water quality problems?

What mistakes have I made and what should I have done instead?

How do I rescue the current situation?

1. What is actually going on in my pond to cause the water quality problems?

Your pond is experiencing classic New Filter Syndrome (NFS), which unfortunately is being compounded by the small volume of your pond and the relatively high stocking density.

What is New Filter Syndrome?

New Filter Syndrome is a technical term used to describe what can happen if a new pond such as yours is stocked in haste. It is understandable that having spent many creative hours designing and building your new pond, that you are eager to see it as you intended – thriving and well stocked with beautiful koi. However, in your rush to achieve the finished result you could easily overlook some basic principles of fish husbandry, leading to a case of NFS.

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 stressing your fish.

This doesn’t happen in most other ponds, so why did it happen in my new pond?

New ponds are relatively lifeless. Constructed out of inert materials (such as your new pond liner), and filled with water that has been disinfected to make it suitable for drinking rather than fishkeeping. 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 you will experience an imbalance and build up of pollutants and this in essence is New Filter Syndrome, and is exactly what you are currently experiencing.

To confirm this, your tests show that you have unacceptably high ammonia and nitrite readings as a result of the under performing filter in relation to the demands that your fish are putting upon it.

So what? What is the problem with my pond experiencing NFS?

Your pond itself will barely suffer as a result of NFS, but unfortunately your fish will as a result of the high ammonia and nitrite levels in your pond. If your fish are not currently showing signs of distress or disease, then they are likely to do so shortly.

This is because fish excrete ammonia because it is toxic. So, by excreting it into the pond water, your whole pond environment inevitably turns toxic (unless it is broken down at the same rate by bacteria). Typical ammonia intoxication symptoms that you are likely to see in your fish are gasping at the surface, lethargic behaviour, and excess mucus secretion.

If your 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, you will probably find nitrite to be far more persistent once levels have built up in your new pond. Where ammonia levels might eventually drop quite rapidly once Nitrosomonas bacteria have kicked in in your new filter, 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. The accumulation of nitrite in your pond will be causing nitrite to accumulate in their blood as they indiscriminately absorb it through their gills.

This reduces the oxygen carrying capacity of their blood, causing your fish to gasp, flash or scratch through irritation. You’ve been adding salt which will reduce nitrite toxicity, but your best approach is to create a nitrite-free pond – especially as you’ll be diluting your salt content every time you carry out a water change.

What mistakes have I made and what should I have done instead?

Your problems have arisen as a result of adding too many fish too soon, coupled with your pond being very small in size.

You may only have had a small plot available for your pond, but a 200 gallon pond that is only 18″ deep is not suitable for koi and will also limit your pond keeping success in other areas.

You should aim for as large a pond as possible, that is at least 3′ deep. A large pond will help to smooth out any rapid changes in water quality and temperature as well as producing a far more stable pond environment. Furthermore, when stocking a new pond with fish, you should do so gradually, testing for ammonia and nitrite as you go to verify that your pond filter is maturing and functioning in line with your stocking rate.

You must let the filter’s maturation rate set the pace.

How do I rescue my current situation?

a. Partial Water Change

Your huge water change would have been effective at reducing the ammonia and nitrite levels but a water change on that scale would have also stressed your fish. By carrying out smaller partial water changes, 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.

b. Reduce Feeding

You’ve also done the correct thing by stopping feeding (having potentially overfed your fish and pond in the first few weeks). As ammonia excretion is related to the level of protein in the diet, your action will have reduced your filter’s ammonia burden. In addition, should the first partial water change not reduce ammonia levels below acceptable levels, then further water changes would be necessary.

c. Help your new filter to mature.

You can 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 (as you have been doing), or obtaining some mature media (or filter extract) from your neighbouring 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.

New Filter Syndrome is often the first (and most expensive) problem encountered by new pond keepers. In some cases, the consequences can seem so extreme or final with solutions seeming so long tem, that NFS can put people off keeping fish altogether.

Many first encounter it unknowingly in the form of diseased fish, hoping to medicate the problem away. In fact where NFS is the cause of health problems, treating fish will not solve the problem. Fortunately, you’ve been testing your water and have highlighted a water quality problem and by doing so, will hopefully avoid any serious fish health problems. Once your filter has fully matured, you should not encounter any further water quality problems (assuming you do not overfeed or overstock your pond).

Kill blanketweed and string algae.