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Preventative treatment during spring time

Koi care in spring is probably one of the most difficult times for Koi keepers, because most losses occur during this time.

The variations in winter temperature in different regions in South Africa, is such that it is hard to give generic advice that will be applicable to all. The fact remains that whether the winter temperature average at 16 degrees or at 6 degrees Celsius the problems experienced by Koi keepers throughout the country in spring, remain the same. The temperature sensitive bodies of the Koi are going through the same cycle per season and therefore per year, regardless whether the temperature ranges are extreme or mild. It is almost as if Koi are genetically programmed to go through a resting period.

A friend of mine, while still residing in the North Coast of KwaZulu Natal, was very keen on showing Koi. His modus operandi was to buy batches of the best Tosai that he could find and then grow the lot of them on in a special pond that was build specifically for this purpose. This growing on pond also served as a long term quarantine pond for the young fish to guard against any possible disease. He would then release the best fish for showing purposes in his main pond and pass the rest on to hobbyists. The pond was equipped with a heater, protein skimmer, sand filter and an over-designed biological filter. A waterfall and Hiblow 40 air pump provided the oxygen. The temperature was maintained at 24 degrees Celsius to ensure optimal growth of this Koi. The result was the same every year. Like clockwork, parasites and the resulting ulcers will appear in the middle of November (early summer, late spring). Needless to say my friend was utterly dismayed because some of his future hopefuls were ruined and not suitable for showing in future.

Every year was the same old story. I will do the water tests, scrapes for parasites, inspecting the filters etc. Every year we found the same results. The checklist confirmed clean filters, impeccable water conditions, fresh food etc, but there were a cocktail of parasites present.

These problems continued for some time until we started to do a few preventative parasite treatments during the winter and to follow a specific protocol when spring arrives. The fairly simple protocol will be discussed later.

As mentioned numerous times on this web site, there may be those who advocate that no chemicals should be unnecessarily added to ponds and we agree. Over the years however we have found that preventative measures during winter and spring cannot be regarded as unnecessary treatment. In fact, in the interest of our valuable Koi, preventative treatments are essential. Remember the interest of Koi comes first and then the armchair philosophies!

In my experience with koi and disease treatments over many years and in many ponds, I have never seen an uneventful spring/early summer if koi collections have been subjected to stress during the winter such as overstocking, where new additions have been added to a pond or where a new environment has been created by moving collections to new ponds or doing major alterations to ponds during winter time.

Although not all the under mentioned will manifest itself in every pond, the following is the most common problems experienced during spring:

Green water

Green water may actually appear any time of the year but it is most prevalent during springtime. Mostly the appearance of green water is only harmful to the ego of the hobbyist. The Koi enjoy it!

Some of the reasons for this bloom by suspended algae are the following:

The rotifers that feed on suspended algae have died off because their food supply has dwindled during the relative algae free winter months. These plant-eating organisms will only multiply to sufficient numbers to control algae once the food source (algae) has established itself.

The tube of the ultra violet sterilizer needs replacement.

Accumulation of Nitrates over the winter months, and a rise in temperature may act as a trigger for the algae to multiply.

High ammonia/nitrites

At very low temperatures, the biological activity in the filter system has slowed down considerably and the water parameters will fluctuate until the required balance is restored. Contrary to what is believed, Nitrifying bacteria do not die off during cold water conditions, but like the other pond inhabitants go into a state of inactivity. The nitrifying bacteria responsible for converting ammonia to nitrite are the first to respond. The bacteria that convert nitrite to the more harmless nitrate, always lags behind and a window period for a nitrite spike will then occur. The increased feeding rate that automatically follow the arrival of spring, also contribute a sudden increase of ammonia. In subtropical and tropical climates however, the threat of high ammonia/nitrites are not so high.


One of the golden rules in keeping Koi is to remember that you cannot get a Koi to be parasite free. Medication that will kill all parasites will inevitably also kill the fish.
Most parasites flourish and multiply in warmer water conditions. In cold water, these organisms do not just cease to exist. They are always present on fish and wait for conditions to improve. The improved conditions can include an increase in temperature and anything that may stress the Koi like temperature swings, dirty filters and bad water conditions. The exception is the dreaded Costia. Costia remains active even in the coldest conditions and must be guarded against!

Bacterial problems

During spring, the water starts to heat up and the first activity will be at micro level as bacteria have simple structures and can respond quickly to the change in environment. Although experts differ on the exact temperatures, most agree that Koi are most susceptible to disease between the temperatures of 8.3 and 16.8 degrees Celsius. Below 8.3 degrees Celsius, one can say there is a ceasefire in the pond. The Koi’s immune systems are not functioning, but the pathogens are also not very active. Below 16.8 degrees C, the immune system of Koi is not fully functional but the pathogens are relatively active.  Above 16.8 degrees Celsius, the immune system is again functional, and can normally reduce the pathogens, provided the Koi is not already in a weakened state.  The critical range, described by many authors on immune systems, as “Aeromonas alley,” is the range over which the pathogens are active but the Koi’s immune system is compromised. Koi with a compromised immune system, regardless of the cause, will be less able to adequately fight disease. Combined with a good cocktail of parasites as described earlier, it may prove fatal to Koi.


Although it is also a bacterial problem, dropsy is mentioned separately because regardless of the pond and water condition, it is a very common to lose one or two Koi in spring due to dropsy.


To summarize the above, one can say that although the Koi may have seem healthy going into winter, there is a definite chance that they were carrying a low number of parasites. Many Koi change hands during all seasons and even if a Koi has been quarantined, pathogens may come into ponds and only wreak havoc during spring. When in low temperatures the immune system of a Koi is at its lowest, as well is the parasite activity. But, as the water warms, bacteria and parasites become active quicker than the Koi’s immune system. This is a critical time for the Koi.

I have no scientific evidence to support this, but through experience I am convinced that whether Koi comes out of winter in extremely cold areas, or in moderate areas, the perils that they face are exactly the same. It is as if pathogens and Koi are either genetically programmed to go through a resting period, or the activities of pathogens and fish goes through the same “awakening cycle” whether in colder climates or in warmer areas. The cycle just occurs within different temperature parameters.

Preventative treatment

With the above in mind, preventative treatment of a pond during spring is the most sensible way to protect a Koi collection. The following treatment is a preventative measure so it is still crucial to keep a close eye on the Koi’s behaviour and to diagnose any problem early.

The recommended preventative treatment is not limited to higher temperatures and it is suggested that the treatment starts in South Africa as soon as you get some free time after the 1st of September (1st day of spring)

Salt. Add 1 kg of coarse salt for every 1000 litres of pond water. Repeat this dosage on day 2 and day 3 to give you a total of 3 kg per 1000 litres. The salt content of the water will then be 0.03%. At this level, salt will act as a mild antibacterial treatment and it will kill most parasites. The only exception will be flukes and salt resistant strains of Costia. The further advantage of salt is the strengthening of the Koi’s cuticle or slime layer and lessening of the effects of fluctuating water quality. Please maintain a salt level of 0.03% when changing water, until the temperature has stabilised!

    Salinity tester

Seponver Plus. Seponver Plus is a dewormer normally used by sheep and cattle farmers. Although a bit hard to get, this medication can be safely added to ponds containing salt. The dosage for Seponver plus is 4.4 ml per 1000 litres of pond water, followed by another treatment 5 days later of 2.2 ml per 1000 litres of pond water. This dosage will get rid of most flukes!

             Seponver Plus


Try preventative treatment and go through the dreaded spring-time stress-free!

Last Updated on Wednesday, 27 July 2011 20:05