Aeration and filtration are both necessary if you want your koi to reach their full potential. You are probably thinking, “Wait a minute! I’m not sure I want to the amount of breeding that would require me to have to worry about all of this!” Whether you just plan to sell off your excess koi in order to help to offset some of the cost of keeping them, or you have grandiose plans of developing a new variety of Koi right in your backyard pond, you DO need to worry about aerating and filtering the water in that pond.

Treat Your Koi as Your Pet

The Koi you will be keeping in that pond should be considered as much of a pet as your dog or cat. As such, your fish deserve the best of care. That includes water to swim in that has been filtered to remove any harmful material and the waste products from the fish. What would happen to your pond and to your koi if you decided to do without filtration?

Your pond will very quickly turn a sickly shade of green due to algae build up in the water.

  • Fish parasites enjoy murky, algae-filled water, as do other creatures that may well harm your fish. If just one fish in your pond is infected by a parasite or injured by another creature in the water, the chances are good that all of your other koi will experience the same fate.
  • Standing water that is full of algae and parasites really smells horrible and looks pretty awful, too. Do you really think your koi could live in all of that muck? Here is a hint – They cannot breathe or live in water like this.

Choose a Good Filtration System

koi pond filter photo AERATION AND FILTERING NEEDS
Photo by MyLifeStory

You will definitely have to plan what kind of filtration you will use in your pond. Do not try to save money by purchasing the cheaper filtration system. You may well regret it if something goes wrong with the filter and causes you to lose all of your koi. Most experts recommend that you choose a filter that is able to handle 33% of the total amount of water in the pond.

As an example, a pond that is capable of holding 3000 gallons of water needs a filter that can circulate 1000 gallons of water. If you must dip lower than this percentage in order to get a filter you can better afford, you should not choose a filter that circulates less than 10% of the total water volume.

Your pond filtration system should consist of two types of filtration. These are –

  • Mechanical filtration
  • Biological filtration

 How Filters Work

Mechanical filtration works by trapping debris and fish waste as they flow through the water with the use of brushes, pads, sand, or small beads. Biological filtration involves a natural method that changes the fish waste into amalgams that will not hurt the fish. All koi have ammonia in the excretions, and a build up of ammonia can kill any fish. Bacteria that are present in a biological filter change the ammonia and nitrates in the pond water to nitrites, which are safe for koi.

Your filtration system will also need a pump. You have two choices of what type of pump to place in your koi pond. The types of pumps available are –

  • Submersible
  • Recirculating

The submersible pump is a good choice for a smaller pond. If your pond will feature a waterfall, a submersible pump can be used to handle the volume of the waterfall alone.

A recirculating pump is usually what is used for good-sized ponds. They are sturdy and efficient, and most will serve you for a long time.


Your Koi need oxygen to breathe, just like you. Aeration places oxygen in the water so that the fish can breathe it in through their gills. If there is no aeration, there will be no oxygen, and the fish will die. If you are keeping too many koi in a small pond, or if there is an overgrowth of algae, oxygen levels are rapidly depleted.

koi pond water falls photo
Photo by gosheshe

You have probably seen koi ponds that feature a beautiful waterfall. Pretty as it is to look at and to hear, that waterfall is not there for looks only. The constantly moving water helps to aerate the pond. If a waterfall is not for you, plan to purchase an air pump. This, along with one of the pond accessories that bubbles, can help you to get oxygen into your koi pond.


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