Main Causes of Non-Disease Death in Koi and How to Solve Them

I. Water Quality Problems

Currently, household koi keeping mainly uses tap water. In some areas, the source water for tap water is of poor quality, and water plants use large amounts of disinfectants and cleaning agents during treatment. After a water change, the fish cannot adapt and become poisoned, which is why water treatment steps such as sunning and aerating the water before a change are necessary. Chlorine in the water is the main cause of fish poisoning. During water changes, a gradual step-by-step method should be used as much as possible, completing the change in several stages, and an appropriate amount of sodium thiosulfate should be added to remove residual chlorine from the water.

Koi prefer to live in water with low hardness, but both soft and hard water can be used to keep koi. Generally speaking, tap water is soft water, while groundwater (spring water, well water) is hard water. When transporting fry or keeping koi, avoid suddenly moving them from soft water into water with higher hardness, so as to prevent allergic reactions in the fish.

Water color can reflect the quality of the water to some extent. A tender green water body indicates relatively good water quality. Timely daily removal of waste, or regularly adding photosynthetic bacteria to the water body, can keep the water color clear and fresh.

II. The Problem of Temperature Differences in the Environment

Although koi can survive at water temperatures of 2-30°C, they adapt very poorly to sudden instantaneous changes in water temperature, and a temperature difference exceeding 3°C can easily cause sudden death.

After the fry are bought, they cannot be immediately released into the fish tank or other water body. Generally, the koi fry should first be placed together with the bag they are in into the water where they will be kept for 20 minutes, then new water should be slowly added into the bag, gradually replacing the original water in the fry bag. This process is commonly called "tempering the fry" and can effectively reduce sudden death of fry caused by temperature differences.

During keeping, sudden changes in water temperature must also be prevented. In household keeping, when the weather is cold (especially in northern regions), if emergency water changes are needed, the new water can first be heated with a water heater, slowly added into the fish tank, and a thermometer used to measure temperature changes in real time.

III. Poisoning Caused by Excretory Waste

Due to the metabolism of koi, excreted waste and leftover bait settle in the water body. Harmful substances such as nitrite, ammonia nitrogen, and hydrogen sulfide produced from this waste through various pathways dissolve into the water. After continuous accumulation, they cause the koi's constitution to decline and lead to poisoning. When the concentration of harmful substances is too high, the koi's activity weakens, they float to the water surface, their body color fades, and then large numbers of deaths occur. The accumulation of these harmful substances not only poisons koi to death, but also breeds large amounts of various pathogens, which is also one of the main causes of fish disease. The solutions mainly involve the following aspects:

1. Carefully Choose Feed

Some feeds have spoiled animal bone meal and carcasses added during production. These feeds easily produce ammoniated compounds after being fed, so feed with a rotten smell should not be chosen when purchasing.

2. Control the Feeding Amount

Controlling the feeding amount is an important part of keeping koi well. Leftover bait produced by overfeeding not only causes waste, but also rots and produces harmful substances, threatening the survival of koi and also making it difficult to maintain their body shape. Generally, feeding should be controlled so that the fish finish the food within 10-20 minutes, and the bait must not be fed in excess. Whether feeding is excessive can be observed through the koi's feces; if the feces become hard, it indicates overfeeding. The best feeding frequency is once in the morning and once in the afternoon (in summer, feed should be given in the morning). Feed mixed with fish meal and malt is relatively easy to digest, and a few tablets of digestive enzymes can also be mixed into the bait to aid digestion.

3. Add Salt Appropriately

When adding water, adding salt to the new water at 0.2%-0.3% can both inhibit the growth of some harmful bacteria and provide salt for the fish's own normal metabolism, reducing the production of waste.

4. Add Microorganisms to Decompose Pollutants in the Water

Microorganisms such as nitrifying bacteria, photosynthetic bacteria, and Bacillus subtilis can decompose koi feces and leftover bait, depriving pathogens of nutrients. Regularly sprinkling these beneficial microorganisms can effectively reduce the content of nitrite and ammonia nitrogen in the water body, so they are also called "water-purifying bacteria."

When using water-purifying bacteria, pay attention to keeping the water temperature above 23°C; the pH value should be above 7.0, as acidic water is not conducive to the growth of water-purifying bacteria. Water-purifying bacteria are live bacteria, and medications have a killing effect on them, so they must not be used at the same time as disinfectants and bactericides. If bactericidal agents or agents for treating fish diseases must be used, wait at least one week or more after application before using water-purifying bacteria. When using photosynthetic bacteria, also note that they should not be used on cloudy and rainy days, so that they can form a dominant community in the water and produce the best effect. In addition, if different water-purifying bacteria are to be introduced at the same time, attention should be paid to their mutual compatibility. For example, nitrifying bacteria and photosynthetic bacteria are not suitable for being introduced into the same aquarium at the same time, because their water purification processes inhibit each other and may reduce their purification effect.

5. Strengthen Cleaning of the Filter Box

During keeping, the filter box generally needs to be cleaned 1-2 times a day. When cleaning, turn off the circulation pump, open the drain pipe of the filter box, completely empty the entire box, and then use a separate pump to flush the dirt off the filter material. If too much dirt accumulates in the filter box and bacteria cannot decompose it in time, the water becomes turbid and produces foam. This foam is mainly caused by excessively high levels of bacteria, organic matter, and ammonia nitrogen waste.

IV. Death of Koi Caused by Oxygen Deficiency

Koi are relatively sensitive to dissolved oxygen, and large-scale reproduction of green algae and moss in the water body affects dissolved oxygen. Aquariums should be kept away from windowsills as much as possible, and lighting duration should be strictly controlled, preferably 8-10 hours a day. Do not use continuous lighting for more than 13 hours, as this causes aquatic plants to grow rapidly and leads to insufficient oxygen in the water. The death of moss and the carbon dioxide and hydrogen sulfide gas released by aquatic plants in the absence of light also pollute and poison the water body, leading to the death of koi. Fish tanks that do not cultivate water-purifying bacteria can be equipped with ultraviolet sterilizers to kill bacteria and algae.

In addition, the keeping water temperature should not be too high; the higher the water temperature, the more oxygen koi consume through metabolism.

V. External Injuries and Death Caused by Jumping Out of the Tank

Koi jumping out of the tank is also one of the common causes of abnormal death. Koi are fish that love to jump and are very strong, so it is best to have protection on top of the fish tank. If the top edges of the tank have many sharp corners, use glass or a soft board to block them. When keeping them in an aquarium, never suddenly turn the top lighting equipment on or off, otherwise the koi are easily startled, leap out of the water, and hit the tank cover or walls, causing external injuries.