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Effects of medications on a koi pond.

I found it difficult to follow and understand, could not see at the time why I needed it and having scraped through the exam promptly forgot most of it - O Level Physics!

One law I do remember though (and thank you Chopper Williams, for explaining it so vividly with your ruler - ouch!) is that to every action there is an equal and opposite reaction.

Mr Williams used many descriptive examples (besides corporal punishment) to illustrate this, from the harsh recoil of a gun to the boxer putting his opponent on the canvas with a right upper cut.

A similar trade-off between two factors is also found in the world of medicine where the trade-off is made between cost and benefit Many areas of medicine have costs for the patient (both financial and in possible side effects) but also benefits that hopefully outweigh any costs.

The fewer or lighter the costs, the more likely it is that such a treatment would be used (Eg Taking Paracetamol for a headache)

Further up the scale where side effects are more noticeable (but still a price worth paying), treatments such as using antibiotics to keep infection at bay may be considered, but at the price perhaps of an upset stomach. More extreme still are treatments such as chemotherapy to control cancerous cells or even amputation for sufferers of gangrene.

As the health complaint gets more serious, there are generally greater side effects to contend with during treatment. In any case, having elected for a particular route, certain counter measures can be taken to reduce the impact of any predictable and unavoidable side effects.

There are obvious parallels in the world of Koi where there may be a number of treatment options available to us, each for a different ailment or disease. Many we will use quite casually, recognising that risks to koi are minimal, while other methods of treatment are less friendly and may well lead to complications later on.

Nevertheless, any treatment (however traditional or widely used) will bring effects to the pond as well as the koi. If this were not the case, then there would be a strong case for the continuous treatment of koi, using medications to prevent rather than control. In certain circumstances this can be a prudent approach to maintaining koi health (routinely dosing against fungus and bacteria in spring and autumn), but on the whole, medications and pond treatments should be used with care, being fully aware of their impact on water quality and koi health.

Fish out of water?

In many respects, fish are unique when compared to other animals in the pet world. Koi are kept in an environment that is alien to ours, making interaction very limited, and they can also quite happily go months without feeding.

Try that with a cat or dog and the RSPCA would be likely to call.

Fish also differ from other animals in that when they are ill or in need of treatment the fish itself is not treated, but rather its environment. Straight away alarm bells should start to ring as the recognised route to koi success is through a stable and quality environment and dosing their pond with chemicals is hardly going to achieve this. Furthermore, unlike a more mobile terrestrial pet that can soon move from an unhealthy or threatening environment, fish are trapped in the pond in which they are kept - experiencing fair weather and foul, whether they choose to or not.

Treating the water does have its benefits (for example, you can treat 30 koi or 300 koi for the same price if they are kept in the same water volume, but overall the risks to the koi, through unwelcome variations in their pond water quality are real when treating a pond and must be addressed.

Treatments that are used against disease organisms or unwanted algae are effective through their detrimental effects on living organisms. Some treatments (certain algicides) are very specific to their target pest and will not pose a direct threat to koi health while others may be so active that they will even threaten the beneficial bacteria and protozoa in a filter. In certain cases, medications can even pose a threat to the koi keeper.

Nearly all treatments will cause similar general side effects to a ponds water quality, irrespective of their mode of action. Other treatments will have an indirect effect (by the impact of any dead or decaying by-products) and some will have very specific impacts on water quality, brought about by their specific chemical nature.

Such side effects can be placed into 1 of 4 groups.

Drops in DO due to an increase in solutes.

There are limits to the quantity of dissolved substances (solutes) that can be dissolved into a solvent. In a koi pond, the solvent is of course, water which will carry any number of solutes. These will include dissolved solids such as amino acids, sugars, minerals and salts as well as dissolved gases (ammonia, oxygen etc). One of the most important solutes is oxygen, but unfortunately, as a gas, it is more volatile than dissolved solids and is more likely to be one of the first to rise out of solution when other solutes are added to a pond. Consequently, when a medication is added to pond water, the DO levels are likely to drop, putting fish, bacteria and protozoa (who all require oxygen) at risk of stress.

To reduce the risk of further stressing Koi, add extra aeration during any medication.

Effects on biofilter performance.

As mentioned earlier, the most popular medications are those that are effective and have the most acceptable side-effects. One of the least desirable side-effects for a koi pond would be to harm the biofilter. Where a pond treatment is a short term remedy for a disease or water quality problem, if that short term remedy causes further long term problems by adversely affecting the filter bacteria then such a side-effect is unacceptable. There are a number of medications to be wary of due to their negative effects on filter performance. (Table 1).

Table 1. Effect of Medications on Freshwater Biofiltration

Medication Concentration (mg/l) % Filter Inhibition
Oxytetracycline (Antibiotic) 50 0

Erythromycin (Antibiotic)

10 100
Formalin 6-10 0-27
Malachite Green 0.1 0
Formalin + Malachite 10+0.1 0
Methylene Blue 5 100
Potassium Permanganate 1-4 0-86

For this reason, when using those medications with potential to cause harm to a filter, be sure not to use too high a concentration. The observation that the most commonly used medications are those that do not have a significant detrimental effect on biofiltration is no coincidence.

Indirect effects through dead or dying organic matter.

All organic matter attracts the attentions of heterotrophic bacteria that break it down for food. These organic-loving bacteria will thrive and multiply in conditions where there is an excess of organic matter, demanding lots of oxygen as they do so. The higher the organic load in a pond, the greater the demand for oxygen - leaving less for koi and nitrifying filter bacteria.

Many treatments are themselves organic-based compounds which will be broken down by bacteria. Furthermore, many treatments can cause a build-up of dead or dying organic matter. Algicides or anti-parasite treatments can lead to an accumulation of dead algae or mucus that has been sloughed off, causing a drop in DO as bacteria thrive and breakdown these organic compounds. To avoid such problems, remove as much algae prior to and after treatment from the pond and aerate the water vigorously during medication.

Chemical interactions with the pond water and koi.

Pond water is literally a cocktail of different compounds dissolved in water. The addition of a chemical treatment will have an undesirable side-effect of changing from the preferred water quality composition to which koi have become accustomed. This is unavoidable, but each time medication is added, we should be aware that koi are likely to be stressed by the resultant change in water quality. The active ingredients of a chemical treatment will react with other solutes in the pond forming other compounds (the reason why the water remains dyed longer in ponds containing softer water). In addition, malachite green for example, is unavoidably absorbed by Koi through their gills, having an undesirable and cumulative effect on a Kois physiology. The more frequent the dosing, the more koi will be stressed.

Medications are not usually selective in their action but quite crude, with fish surviving by virtue of their size and complexity in relation to the susceptible pathogen. Consequently, pathogens of just 1 or a few cells in size are easier to treat than the more complex and larger parasites.

Medications are nearly always toxic to fish and humans and administered on the basis that at the recommended dose rates, they are more toxic to the pathogen than the fish. This is why medications should never be overdosed.

We are often too keen to dose pond water with chemical treatments, and it is essential to acknowledge that while most disease problems are the result of a water quality problem, aquatic medications will not solve a water quality problem but only treat the disease. Therefore always try to identify and solve the cause of the problem before adding a treatment. You may be stressing your Koi unnecessarily.



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