In a koi pond of 3 m x 4 m or 12 m3, you can keep at least 3-4 koi of 20-45 cm in length. The population of goldfish relatives is indeed small, but koi will live comfortably in ponds. Please note that Koi needs 1 m3 of space per head. But the koi population in the pond can be denser if the size of the koi kept is between 15-20 cm. The population can reach 6-8 heads.
When the size of 6-8 koi becomes large, the density of fish in the pond automatically increases. However, this is not a problem as long as the water quality of the pond is maintained. The trick is to increase the filter capacity from the beginning. In a normal pond, the filter capacity is sufficient for 30% of the pond volume; in a fixed pond it is 40%. The goal is that the ammonia from the leftover food and manure, which increases with overpopulation, does not poison the fish.
The filtration system consists of at least 4 filter chambers along the length of the pool. In the front chamber, the water first enters the vortex. It then passes through 2 biological filters, each containing 10-15 sheets of mat. Next, the water enters the 3rd chamber containing the Bioball. When the water comes out of the last filter, a 40-watt ultraviolet lamp is used to kill any remaining bacteria.
To increase dissolved oxygen, the water from the last filter is pumped into the pool like shower water. If dissolved oxygen is low, it can be increased by adding aerators to each filter chamber.
As a reminder, filters in heavily populated ponds need to be washed at least once a month to keep dirt and bacteria from settling. Especially if the pool is outdoors. Rain causes the pool water to become more acidic, which causes ammonia levels to increase. Another treatment is to backwash 5% of the pond water per day, allowing new water to enter.
It is also necessary to add salt to the pond, the dose is 2-3 kg/ton of water. Salt has the function of releasing mucus in the body of the Koi and stimulating the appearance of a solid color. Salt can also neutralize water. Salting can be done periodically every 1.5 months.
Formula for calculating ideal number of koi in a pond
Number of koi = (pond length x pond width) / average koi size / 150
Number of koi = (pond area / 2) / average koi size