Keeping Koi in Your Outdoor Pond

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The ponds are alive with plants like water lilies or water lettuce and animals such as fish, frogs, dragonflies, turtles … Fish are beautiful and useful as they eat larvae that mosquitoes lay in the water.  Koi is perhaps the most popular pond fish. It is a variety of the Asian common carp, Cyprinus Carpio.


You must provide a stable environment with a regular routine that is not stressful to its inhabitants. In nature, fish are accustomed to a gradually changing environment. Water chemistry also has continuity that the fish are accustomed too.

You need a large pond because koi get quite large despite the size of the pond, it is recommended that a koi pond be no less than 1000 gallons in volume, the bigger the better. It also needs to have an area of the pond at least 3 feet deep, 4 – 5 may be better. Fish are not happy in shallow water, because in summer the temperature is too high and oxygen is scarce. They can live with peak summer heat, although it is advisable to have the shadow of water lilies and other aquatic plants.

Also there will be no problems during the winter if ice forms above. Small koi seem to survive winters better than larger koi. This is due to the fact that the former can survive in lower oxygen concentrations.  With temperatures below 15ºC they swim to the bottom and only go to the surface to nourish. As long as they have 70 cm of free water they stand up to 2 ° C and with an ice coat on top. You should break it to let them breath. When the temperature drops below 10 ° C is not advisable to feed the fish.

The success of your pond will rest primarily with the water quality. If water is tested regularly, poor conditions can be rectified before things degenerate. The big key to understand about water testing is that it will reveal potential problems before the fish show signs of distress. The pH value should be around 7 to NO2 and NO3 as close to 0, that value being the ideal. Poor water quality will result in fish illness and possibly death.

Keep optimal water quality control parameters.  “Less more frequently” is the general motto for changing water. It is a great idea to perform water changes on a weekly basis. Monthly can suffice for well filtered ponds. It is better not to change too much water at a time – 10-20% is the norm. You need to be aware of the potential temperature change you will create as well. Avoid a temperature change of more than 2Celsius.

When cleaning the filter use pond water, not cold chlorinated city water. If you are power washing your filter media on a weekly basis, you are actually destroying beneficial bacteria. The pond water may be clear with this approach, but clarity does not mean it is chemically clean for the fish. The keys to filter maintenance are to clean the media with pond water and not to over clean.
If you don’t have a UV Sterilizer, your pond will typically experience an algae bloom during Spring. The water turns green, sometimes with visibility of just a few inches. The bloom will run its course and usually clear on its own. Changing the water and scrubbing the liner is not the answer, and is totally counterproductive. This simply resets the cycle and destroys organisms that actually consume algae.

Without a UV Clarifier, algae blooms will die back in time as your plants and filter mature. Additionally, make sure to maximize aeration as this drives out CO2, essential for plant photosynthesis. It also provides oxygen to the fish, particularly at night when the algae are consuming oxygen through respiration.


You cannot generalize, but most of the time you can’t put as much as you think. Do not overcrowd your pond, because water quality will go down. Even if the water quality is good, when you start stocking over 3 lb. of fish per 100 gallons, you are inviting trouble.

Purchase and introduce cautiously new fish. Koi get sick first and foremost from the inoculation of parasites by the introduction of an infected fish. Purchase only fish that shows no signs of disease or malformations. A fish in good health is stirred and moves. Extreme caution needs to be exercised. This means you should quarantine or buy from a reliable source that has quarantined and performed a microscope analysis. Your water quality should be impeccable before adding fish, and new fish should not be introduced during the spring because your current population is weakened from winter.

Being able to spot ailing fish quickly is paramount. Then you need to get a proper diagnosis. Remember that buying meds based on mere conjecture can do more harm than good. Water testing and performing a mucous scrape to view under the microscope ensure you find out what is really going wrong. Ideally a slime coat analysis is done routinely with a scope so that small problems can be rectified immediately. This allows you to take informed action to correct the issue.

Nutritional Requirements

Koi are omnivorous. When in the wild or in more natural ponds with lots of algae and mud bottoms, they do very well on their own and require little or no supplemental feeds. However, once they are put in an artificial setting which is filtered to be kept clean and dosed with algaecides to keep the algae at a minimum, many of the natural foods are removed and they become dependent on their keepers for nutrition.

In general, it is a good idea to feed Koi a variety of foods to be sure that all required nutrients are accounted for. Most quality feeds on the market are more or less complete and the fish will do well on them, but a vitamin or mineral may be missing or low. Therefore, if you feed multiple diets you stand a better chance of covering all the requirements. This can be done by mixing pellets together or feeding two foods on alternate days. However, for the fish to excel, they should have a variety of foods, including live.

This article was written by Guizmo