I. Water Quality Requirements for Park Koi Ponds
(1) The pond water must be odorless, free of foul smells, and non-decomposing.
(2) The water should be moderately fertile, with a transparency (clarity) of about 1 meter. Water that is too shallow may cause fish to surface for air (hypoxia) and die, while water that is too deep may hinder the growth and development of koi.
(3) It is best for the pond walls to have a small amount of algae growth. Excessive algae should be removed promptly.
(4) There should be no unusual bubbles rising from the pond water.
(5) Chemical measurements of the pond water should meet the following standards:
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pH: 6.8–7.4
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Hardness: ≤15°dH
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Iron ion concentration: ≤0.3×10⁻⁶ mg/L
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Sulfate ion concentration: ≤15×10⁻⁶ mg/L
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Chloride ion concentration: ≤19×10⁻⁶ mg/L
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No residual chlorine
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Dissolved oxygen (DO): ≥5×10⁻⁶ mg/L
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Ammonia: ≤0.1×10⁻⁶ mg/L
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Nitrite: ≤0.1×10⁻⁶ mg/L
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Nitrate: ≈5.5×10⁻⁶ mg/L
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No hydrogen sulfide (H₂S)
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BOD (Biochemical Oxygen Demand): 2.5–7 mg/L
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Turbidity: ≤5 NTU
II. Construction of Koi Ponds
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Pond Construction RequirementsWhen constructing a koi pond, factors such as sunlight exposure, wind direction, rainfall, safety, and dust fall must be considered. The minimum pond area should be 15 m². For large koi, the depth should be 1.5–2 meters; for small koi, 0.8–1 meter is sufficient. The water volume should range from 20 to 50 tons. There are no specific requirements for the shape or structure of the pond.Most modern koi ponds are equipped with biological filtration systems, making maintenance and management easier. Since this is a long-term investment, it is advisable to hire experienced professionals to design the pond. Selecting a reputable koi farm that provides reliable after-sales service is crucial to avoid wasted time and costs due to design changes.
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Steps for Preparing Water in a New PondAfter constructing a beloved koi pond, many enthusiasts may rush to introduce koi. However, experience shows this can lead to fish mortality and significant losses. Therefore, it is wisest to prepare the water (i.e., adjust water quality) before introducing koi. The general steps for new pond water preparation are as follows:(1) Fill the pond with water and scrub it with 1 liter of glacial acetic acid per 1 meter of water depth.(2) Run the bottom pump for 6–8 days to dissolve silicates from the cement into the water.(3) Drain the water and rinse the entire pond 2–3 times with clean water to ensure no glacial acetic acid remains.(4) Place various filter media in the filter tank and fill it with clean water.(5) Add 5 kg of coarse salt per ton of water, then start the pump and aerator.(6) After running the pump and aerator for 3–5 days, introduce inexpensive koi for testing.(7) Test the water quality to ensure it meets the following requirements: pH 7–7.5, dissolved oxygen (5–8)×10⁻⁶ mg/L, ammonia ≤0.1×10⁻⁶ mg/L, nitrite ≤0.1×10⁻⁶ mg/L. After multiple observations, if the test koi swim smoothly and actively, display vibrant colors, and feed eagerly, high-quality koi can be introduced into the pond.
III. Construction and Function of Filter Ponds
The water volume of the filter pond should be maintained at 20%–30% of the concrete pond’s total water volume. For larger ponds requiring larger filter tanks, multiple interconnected filter tanks can be installed for higher efficiency. When setting up multiple filter tanks, a parallel and interconnected design is recommended. Water enters from the top of the first filter tank and exits from the bottom of the last filter tank. If space permits, constructing a water channel approximately 30 cm wide between the filter tank and the concrete pond is far better than using plastic pipes. The longer the channel, the better. If the channel can be designed creatively to enhance the park’s scenery, it would be ideal. Such a channel allows circulating water to fully contact air, softening the water and dissolving oxygen from the air. Lining the channel with limestone or zeolite allows filter media to host nitrifying bacteria, further purifying the water.
IV. Auxiliary Equipment for Keeping Koi
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Water ChannelWhether using groundwater or tap water, it is best to pass it through a water channel before entering the koi pond or filter tank. This allows the water to contact air, quickly improving its quality. For example, groundwater has low oxygen content and high hardness. If it enters the filter tank without passing through a channel, the oxygen-deficient water may foster harmful bacteria and fail to meet water quality standards. Passing through a channel increases oxygen levels, raises pH, reduces hardness, and improves water quality. If a channel is not feasible, aeration methods can achieve similar effects.
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Water SourceThe water source must be safe and reliable, meeting national fishery standards, with an ample supply. Especially in summer, sufficient water must be ensured. Adding an adequate amount of fresh water to the pond stimulates koi appetite.
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Water PumpThe water pump must be energy-efficient, safe, and highly effective.
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Other Auxiliary Equipment(1) Aeration devices, such as air compressors; recently, Japan has begun using ultrasonic bubble generators.(2) Shading devices for concrete ponds (e.g., corrugated plastic sheets to block strong sunlight).(3) Koi nets and floating boxes.(4) Plastic water tanks.(5) Automatic feeders, etc.
V. Management of Park Koi Ponds
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Variety Selection and CombinationIn park ponds, where the water surface is broad, people can view koi from above and appreciate their full appearance and posture. Therefore, varieties such as Kohaku, Taisho Sanke, Showa Sanke, Ogon (Gold), Platinum Ogon, Shusui, and Asagi are typically combined. In aquariums, where only the side view is visible, reflective varieties like Ogon, Platinum Ogon, Matsuba Ogon, and Yamabuki Ogon can be selected, combined with German carp varieties. Whether kept in earthen ponds or aquariums, brightly colored koi should dominate, supplemented by darker, glossy, and elegant varieties.
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Types of FeedKoi are omnivorous and can be fed animal or plant-based feeds such as daphnia, tubifex worms, small shrimp, cornmeal, broken noodles, vegetables, or even rice balls. To enhance their coloration, in addition to proper lighting, background, and water quality, feeding high-nutrition specialized color-enhancing koi feed (available in flakes or pellets) is crucial.
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Feeding FrequencyFeeding frequency varies with water temperature. Refer to Table 2 for details.
Table 2: Feeding Frequency at Different Water TemperaturesWater TemperatureFeeding FrequencyWater TemperatureFeeding FrequencyBelow 10℃No feeding18~19℃2~3 times per week10~13℃1~2 times per week20~22℃3~4 times per week14~15℃1~2 times per week23~26℃5~6 times per week16~17℃2~3 times per week26~30℃1~3 times per week -
Daily ManagementRegularly inspect the pond surface and remove debris blocking the water outlet to ensure floating debris can be discharged. Promptly clear fallen leaves from the water to prevent water quality deterioration. Drain bottom water from the pond or filter tank daily. Use backwashing to clean the filter tank, expelling harmful substances such as koi waste, leftover feed, and suspended impurities from the pond.In spring, cover the koi pond with plastic film to stabilize water temperature and prevent sudden drops. Feed high-quality, palatable feed, ensuring a balance between animal and plant-based feeds to maintain nutritional balance, aid recovery, and promote growth.In summer, install shading covers over the pond to prevent excessive water temperature rise.In early autumn (August–September), increase feeding to ensure koi are well-fed. Emphasize animal-based feeds in the diet to help koi safely overwinter.During winter, focus on maintaining water temperature to prevent koi from freezing due to low temperatures. Feed appropriately to prevent weight loss and reduce the risk of diseases.
