Tips for Keeping Koi in Garden Ponds

By JamesM April 23, 2025 0 comments

I. Construction of Concrete Ponds

The pond should ideally be located close to the house for convenient feeding and viewing. Avoid planting large deciduous trees nearby to prevent fallen leaves from deteriorating water quality. The pond should be built in a sunny, sheltered area, with 2–3 hours of daily sunlight exposure being optimal.

Concrete ponds are mostly square or rectangular, with a recommended area of 15–35 m² and a depth of 1.2–1.8 m (minimum 80 cm). Square ponds are easier to manage. During construction, bricks are first used to form the structure, followed by a cement coating. To prevent leaks or seepage, the cement coating should generally be applied in four layers.

If built indoors, ventilation and lighting for the pond must be considered. The shape and size of the pond can be customized as needed. The inner walls should be smooth, and the surface area should be as spacious as possible. Avoid using rough or uneven stones to prevent injuring the koi, and try to eliminate stagnant water areas (i.e., water that remains unchanged for extended periods).

Once the newly built pond has hardened, it can be filled with water but must not be used immediately. Since cement contains significant amounts of alkaline salts, these must be neutralized before introducing koi. Typically, after filling the new pond, add about 50 grams of glacial acetic acid per square meter, mix thoroughly, and drain after 24 hours. Repeat this process once more, drain after 3–5 days, then rinse with fresh water 2–3 times. Finally, introduce some inexpensive koi to test water safety. If the test koi show no adverse reactions, high-quality koi can be introduced.

II. Types of Filtration and Construction of Filter Ponds

(I) Types of Filtration

Filtration for garden koi ponds is divided into physical, chemical, biological, and plant filtration.

Physical Filtration

This involves using various filter materials or aids to remove dust, colloidal particles, suspended solids, leaves, and other debris from the water to maintain clarity. A traditional and simple method is sand or gravel filtration to remove visible suspended particles.
Chemical Filtration

This uses filter media to absorb and remove dissolved harmful ions, compounds, or odors from the water. Common media include activated carbon, maifan stone, and zeolite, as well as ion-exchange resins.
Biological Filtration

This relies on beneficial bacteria attached to filter media to oxidize and break down waste products like fish excrement, leftover feed, and nitrogenous organic matter or ammonia. Common media include bio-brushes, filter wool, bio-filaments, and bio-balls.
Plant Filtration

This utilizes plants to absorb harmful factors from the water. Aquatic plants like duckweed, with their extensive root systems, not only aid filtration but also absorb iron ions and pesticides from the water.

(II) Construction of Filter Ponds

A pipe is connected from the deepest part of the koi pond to a sedimentation tank. After passing through various filter media, the water is pumped back into the pond via a circulation pump for continuous filtration. The sedimentation tank is the first section of the filter system, where suspended solids and heavier metal ions settle. A drain valve at the bottom allows for the removal of accumulated sludge.

The filter pond should be 1/5 to 1/3 the size of the koi pond; larger filter areas improve filtration efficiency. When adding tap water or groundwater to the koi pond, it should first be introduced into the filter pond to soften the water and reduce residual chlorine levels, rather than being added directly to the koi pond.

Since biological bacteria require oxygen for decomposition, the filter pond must be equipped with an aeration system to increase dissolved oxygen levels. Air compressors are commonly used to inject air directly into the water, or pure oxygen may be added. For outdoor ponds exposed to intense sunlight, UV sterilizers can be used to control excessive green algae growth. Alternatively, shading devices like shade cloth or corrugated plastic sheets can cover about one-third of the pond to prevent UV rays from affecting water quality and koi coloration.

III. Tips for Keeping Koi in Garden Ponds

Maintain Adequate Dissolved Oxygen

To prevent hypoxia, use air pumps or compressors to aerate the pond water.
Keep a Small Number of High-Quality Koi

Raising a limited number of high-quality koi is a key principle for successful koi keeping.
Implement Bottom Drainage and Three-Dimensional Water Exchange

Drainage pipes must never be placed near the top of the pond. Water exchange should be three-dimensional, allowing harmful factors to be expelled from the pond as early as possible. This promotes vibrant coloration and healthy growth in koi.
Improve Water Quality with Biological Filtration Cycles

Generally, genetic factors account for 50%–70% of koi quality, water quality for 20%–30%, and feed for 10%–20%. This highlights the importance of maintaining excellent water quality.
Foster a Pond with Thriving Algae

"Water conditioning" is crucial—creating "mature water" with abundant algae. Combining biological, physical, chemical, and plant filtration helps soften new water quickly and purify existing water. This encourages the growth of green algae on the pond walls, a sign of good water quality.
Eliminate Parasites

External parasites like anchor worms and fish lice can be detected through careful observation. Infected koi may cluster in corners, rub against each other or the pond bottom, lose appetite, become weak, and succumb to secondary infections. Commonly used treatments include trichlorfon, with dosage adjusted based on water temperature and koi condition.
Winter and Spring Management

In winter and spring, water temperatures often drop below 20°C, reducing koi activity, feeding, metabolism, and digestive function. Feed should be reduced accordingly. During these seasons, closely monitor koi health and prioritize parasite control. Early spring is particularly critical, as temperatures rise abruptly and koi immunity is low, making them vulnerable to diseases. Disinfecting pond water and koi, along with maintaining clean water, is essential.
Summer and Autumn Management

In summer and autumn, higher temperatures increase koi activity, feeding, growth rate, and color vibrancy. Feed small amounts multiple times daily, avoiding expired or spoiled feed. Particularly in autumn, koi feed vigorously to build nutrient reserves for winter. Ensure their diet is nutritionally complete and fresh.