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The main factor in successful Koi and other Pond Fish keeping lies in the maintenance of good water quality. pH, ammonia and nitrite levels in the pond should be checked regularly. However, what is seldom mentioned is the details of how 'poor water chemistry' can affect the health of our fish. The most revealing answer usually given is, 'it causes stress!!'. Through understanding how a specific substance present in the water can affect the pond fish's physiology, we can recognise certain behaviour the fish show as a response. With an understanding of good pond water quality (zero ammonia and nitrite level through biological filtration, and pH maintenance via water changing), this article intends to reveal how some of the biological processes the fish relies on are affected by certain chemicals naturally present in ponds.

Ammonia - ideal value in pond = zero

This is a major primary cause of health problems in Koi and other Pond fish. Ammonia is produced from fish wastes, and is excreted from the gills. It is extremely toxic, although its the extent of its toxicity relates to the pH and temperature of the water. In cold water of acid pH the ammonia occurs as NH4+ or ionised ammonia, which is not toxic to fish. Once the pH and/or temperature start to rise the ammonia begins to convert to its toxic form - NH3- unionised or free ammonia. Even very low levels of free ammonia are extremely toxic to fish.

Effects of ammonia poisoning are disturbed osmoregulation (the maintenance of the fish's body salts), as ammonia makes the fish more permeable to water. Ammonia also reduces the oxygen-carrying capacity of the fish's blood and causes gill hyperplasia (excessive growth of new cells at the gills), which further hinders oxygen uptake. Other effects include destruction of mucous membranes, and degradation of the brain and central nervous system. The list of damage cause by ammonia on fish is seemingly endless.

Fish suffering from ammonia poisoning show flicking, gasping, blood streaked fins, eroded body structures. The fish tend to clamp their fins and isolate themselves at the bottom of the pond.

Nitrite - ideal value in pond = zero

Nitrite, produced by the breakdown of waste matter, is extremely toxic to fish due to the effect it has on Haemoglobin, the oxygen carrying agent of koi and other pond fishes blood (haemoglobin is also found in human blood). Any nitrite present in the water will convert haemoglobin to methaemoglobin. This is completely incapable of carrying oxygen. Thus the higher the nitrite level in the water the greater the proportion of methaemoglobin in the fish's blood, the lesser the oxygen-carrying capacity of the blood. As the fish can't get enough oxygen, they increase the ventilation rate and gasp at the surface. Methaemaglobinaemia can be recognised as the blood of the fish turns from vibrant red to a dull brown; this can be seen when examining the gills.

pH - ideal value in pond = 7.0 - 8.0

Koi and other pond fish prefer a pH of between 7.0 and 8.0. Temporary minor fluctuations outside these values cause little harm to the fish, but prolonged exposure to incorrect pH can cause severe health problems to the fish. If the pH of a pond is below 6.0 fish begin to suffer from a condition called acidosis. The acid water causes intense irritation to the fish, and erodes away delicate surfaces such as the gills. This leaves the fish prone to bacterial and fungal infection. Gill erosion also hinders oxygen uptake, causing a condition called Hypoxia - where the Koi are basically suffocating. The agent that carries oxygen in Koi blood (Haemoglobin) is less efficient in acid water. Acid water can also trigger metal toxicity from copper aluminium or zinc. These metals can be present in the water in an insoluble form, but the drop in pH can cause them to dissolve, thus causing toxicity problems to the fish If the pH of the pond begins to rise much above 9.0 then the fish begin to show symptoms of Alkalosis. Here the fish suffer from marked gill and skin erosion, again leaving them prone to infection. Also any ammonia present will be in its toxic form NH3 (see ammonia).

The behaviour of fish suffering from acidosis and alkalosis is very similar. Rapid large changes in pH cause the fish to become very excitable; they thrash around the pond, gasp at the surface, and may even attempt to jump out of the pond. Slower chronic changes are less noticeable behaviourally. The fish will appear listless, show excess mucus secretion, and succumb to numerous parasitic and bacterial infections.

Often fish kept in water of poor quality can show symptoms that resemble those of fish infected with parasites or bacteria gasping at the surface can be caused by low oxygen levels, ammonia/nitrite poisoning, or a low pH, all factors hindering oxygen uptake at the gills and/or oxygen carriage by the blood flicking/flashing/scratching, can be caused by irritation due to chlorine, ammonia, or extremes of pH red wounds can be bought about due to prolonged exposure to a low or high pH. Thus before applying a disease treatment to the pond it is vital to ensure the water quality is good, and is not the cause of the symptoms you have noticed in your fish. Conversely, if the water quality is not ideal then the fish can be more predisposed to parasitic and bacterial infection. It is vital to check your water quality whenever your fish are showing unusual behaviour. If the water quality is poor it must be corrected before any parasite treatments are added. There are many other chemicals dissolved in water that can affect the health of our Koi. For example, heavy metals such as lead can enter the pond; copper can dissolve from plumbing fixtures; pesticides can enter from the garden. There has even been a case of arsenic poisoning of Koi, the source of the pollutant being pressure-treated wood surrounding the pond. All these examples are, however, very rare. Those factors mentioned above are significant to every fish pond, no matter how large or small. The fish are susceptible to poisoning from poor water quality. It is up to us to prevent it happening. This is simple to do through regular water chemistry checks and frequent small water changes. Good water quality is the key to fish health.


Before adding any treatment to your pond or treatment bath:

1 Make sure you have a correct diagnosis of the problem.
Before you can successfully treat any disease it is important to know what it is you are treating. Until you have a correct diagnosis, you will not be able to choose the most appropriate remedy for the problem. Many parasite problems occur because of changes in the water quality. If a disease is suspected, test the water for pH. nitrite and ammonia to make sure there is nothing you need to do before applying the treatment. It is true that many different parasite (or bacterial) infections require the same treatment and it is tempting to put a treatment in the pond just to see if it "does the trick". While this may work many times, it is not "best practice".

2 Remove adsorbent filter material - carbon, zeolite etc.
Nearly all the disease treatments available to fishkeepers have organic active ingredients (even those which claim to contain no chemicals). These organic chemicals are removed by filter materials such as carbon, zeolite etc. So it makes sense to remove them before adding a treatment so that the treatment level is not reduced below the effective concentration.

3 Switch off UV.
As in 2 above, ultraviolet light destroys organic chemicals and, if left on during a treatment, will destroy the treatment. Some treatments may even be made toxic by the action of UV light. Switching off the UV during treatment is a sensible precauton. Leave the UV off for at least a week and 10 days if possible to give the treatment the best chance of doing its job.

4 Increase Aeration - remember that oxygen levels may be lower in the morning.
Many disease treaments can reduce oxygen levels but none of them will be harmed by extra aeration so it makes sense to increase aeration if possible especially if treating during warm weather. Also, remember that oxygen levels may be lower in the morning because the submerged oxygenating plants actually consume oxygen during the night when there is no light. For this reason, always leave fountains running continuously during treatment.

5 Allow plenty of time to observe fish.
It is important to treat sick fish as soon as possible after a diagnosis has been made. However, bear in mind the time of day, as mentioned in 4 above, as well as the time you have to watch the fish after adding the treatment. Never chuck the treatment in the pond and then go straight off to work or out shopping. Even if you have used the treatment many times before, there is always a possibility that the fish may react badly this time and you need to be there to change water or increase air or do whatever is needed if there is an unexpected reaction.

6 Be careful of water temperature.
Adding a treatment to a pond where the water is very cold will probably not do any harm, nor will it do any good. We recommend not treating if the water temperature is below 10 C( 50 F). Of course, if it is an emergency and the fish look likely to die without treatment, you can treat when the water is colder. The point is that, if the water is cold, the metabolism of any parasite, bacteria (and the fish itself) is greatly reduced. As the temperature falls, the fish become dormant and stop feeding. This is because the chemical reactions going on in the fish's body are much slower and not enough to digest food properly. Also, the fish is not using much energy when it is dormant and doesn't need to create more by digesting food. Treatment chemicals will also react more slowly in cold water, or not work at all. So it is unlikely that the fish will benefit from treatment when the water is very cold. If the water is very warm, it has a reduced oxygen holding capacity and adding a treatment may reduce this further thus causing oxygen stress which could make the fish worse. So we recommend avoiding treatments when the water temperature is above 25 C (77 F). Obviously, if the situation is very urgent and nothing can be done to reduce the water temperature, the treatment will have to be used and even more care taken to watch how the fish react.

7 Feeding.
Always follow any specific instructions regarding feeding given on the label of the treatment. If the fish are sick and not eating much anyway it will be better not to feed for a few days at the start of the treatment until the fish recover and are actively looking for food again. If, however, the biological filtration system should be damaged by the addition of a treatment, feeding the fish could cause raised nitrite and ammonia levels which could stress the fish further. Regular, routine testing of the water will show if this is happening and allow you to decide what action, if any, is needed.



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