The Correct Methods and Precautions for Changing Koi Water

Veteran koi keepers have long had the saying that “to keep fish you must first keep the water,” which shows that water quality directly affects the normal growth and development of koi. The purpose of changing the water is also to remove waste from the water (garbage, fish feces and leftover feed, stale impurities), keep the water clean, regulate the water temperature, and increase the oxygen in the water, thereby stimulating the growth and development of koi. To raise koi well, you must have a basic understanding of fish-keeping water:

 1. Raw water: refers to tap water or well water that has just been drawn and has not been sun-dried or treated. Its water temperature often differs greatly from the water temperature in the fish pond (tank), and it contains a lot of chlorine; this water is extremely harmful to koi.

2. New water: clean water from tap water, well water or spring water that has been sun-dried and left to settle for about 2—3 days, and whose temperature is equal or similar to that of the fish pond (tank).

3. Old tank water: the dirty water containing feces and waste at the bottom of the fish pond (tank). This includes rearing water that has not been changed for a long time in the pond (tank).

4. Aged water: the general term for water in a fish pond (tank) that is clean and appears tender green, green, dark green or greenish brown. Among these, tender green water is the best. There is a lot of green algae floating in aged water, and these are also a very good supplementary feed for koi. This water has less decaying and decomposing organic matter and more dissolved oxygen. Fish are often raised in clean, tender green aged water, and the fish raised this way have the strongest appetite, robust bodies, bright colors and very fast development.

5. Clear-again water: if the originally green aged water in the pond (tank) suddenly turns clear, with much of the green algae settling to the bottom of the tank, this phenomenon is called clear-again water. This water easily triggers fish disease and needs to be completely replaced.

 (1) General water change: under normal circumstances, especially in hot summer, as long as you persist every day in gently siphoning out 1/10—1/5 of the feces and dirt at the bottom of the fish pond (tank) together with the old tank water using a rubber hose, removing dust from the water surface and floating feces, and then slowly adding new water of the same temperature along the wall of the pond (tank), the water quality can be kept clean. This water-changing method is not likely to injure the fish and is simple and safe, and is most suitable for household fish tanks or small-pond fish keepers.

 (2) Partial water change: use a folding barrier net to enclose the fish on one side, then gently rotate the water in the pond with a dip net for several dozen seconds, wait for the water to settle for a moment, and then open the drainage gate to slowly release water or use a suction tube to remove the excess fish food, feces and old tank water from the center of the pond (tank), or use a fish net to scoop out the excess fish food from the center, then release 1/4—1/2 of the old tank water, and finally add an equal amount of new water at the same temperature. This method is commonly used as an emergency measure for fish ponds or households when too much food has been fed.

 (3) Complete water change: this kind of water change is often a method carried out together with turning over the pond (tank) and selecting young or adult fish. It is usually adopted only when the water quality has seriously deteriorated, the moss has grown too long, or the fish are too crowded. There are two specific methods: 1. When there is no spare pond available, you have no choice but to scoop all the koi into a basin or place a net cage in the water of a neighboring pond for temporary holding, and add an oxygen-increasing head in the basin or net cage to increase oxygen. Then, scrub the moss off the original pond wall, rinse it thoroughly and cleanly, refill with new water of the same temperature, let it stand for a moment until the water temperatures are equal, and then scoop the fish back into the original pond (tank). 2. If there is a spare pond and new water available, simply scoop all the koi into a basin or net cage, select and handle them separately, divide those that should be divided into separate ponds, and for those not divided, once the water temperatures are equal, move the koi into the new water for rearing. With this water-changing method, special attention should be paid to water temperature, and it is best to choose a clear day before 9 a.m. However, this method is generally only suitable for adult fish or larger young fish, and should not be used for fry. If conditions permit, before a complete water change, you can first fill a spare pond (tank) with aged water, and then scoop the fish directly into the spare pond (tank). In this way, the water temperature changes little, the fish are more likely to adapt to the new environment, and the fish are spared the suffering of being crowded in a basin or net cage. With this water-changing method, in spring and autumn it is generally carried out once about every half month. In the hottest summer weather, when the water temperature reaches above 28°C, when the water color easily becomes very dark and the water quality easily becomes turbid, a complete water change should generally be carried out once every 5—7 days. In winter, when the water temperature drops to around 4°C, koi move slowly, their appetite decreases, and the water quality is not easily spoiled, so unless there are special circumstances, the water is generally not completely changed.