Koi Pond – Oxygen Levels

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Adequate oxygen is essential for the health and survival of your koi fish and other pond creatures. As pond life utilizes the oxygen content of the water, it needs to be replaced. Oxygen enters the water where these two contact each other – primarily at the koi pond’s surface. That is why a waterfall is such a vital adjunct to your water feature.

As the water passes over and splashes against the rocks, it picks up large quantities of oxygen, aerating the water. Aeration can similarly be achieved with a fountain or water pump. These methods increase the area of water coming into contact with the air; in addition, the resulting circulation prevents stagnation of the koi pond.

SOME SYMPTOMS OF OXYGEN DEPRIVATION:

  • Koi fish gasping at the surface for extended periods of time.

  • Overnight death of fish, especially the larger, more sensitive ones.

  • Water that appears murky black and emits an unpleasant odor.

  • Koi fish are attempting to or actually do jump out of the koi pond.

REASONS

  • Oxygen is being consumed by large quantities of decomposing debris on the bottom of the koi pond.

  • Excessive amounts of algae are using up the oxygen during nighttime hours with shorter daylight hours.

  • Too many fish for the size of the koi pond.

  • Surface covered over with lily pads.

SOLUTIONS

  • Remove debris

  • Decrease algae growt

  • Decrease number of koi fish

  • Decrease number of lily pads.

PLANTS

Oxygen is also produced by submerged “oxygenating” aquatic plants and algae. Plants not only help regulate the oxygen levels of your koi pond; they cool off the surrounding area as well. Plants that normally would not survive in direct sunlight or desert climate thrive in the immediate vicinity of a waterfall due to the high evaporation rate. The water splatters and thins out as it rolls over rock, increasing the surface exposure. The resulting evaporating water becomes a heat exchanger, cooling the surrounding air by as much as 15 to 20 degrees. The evaporating water increases the humidity protection to the plants from the harsh rays of the sun.

When adding plants to a waterfall, there are many places that can facilitate plants, such as baby tears and different types of moss. Places that would not be conducive to actual water plants could be flat or craggy areas that receive splashing, providing the necessary moisture for the moss, baby tears (Soleirolia soleirolii) or Isotoma fluviatilis. Other water plants that do not require a specific root base can be placed almost anywhere in a waterfall such as water pea, parrot feather and watercress.

An attribute of moss or baby tears is that it does not require a large quantity initially to look great. If it receives the proper amount of moisture, it will spread and grow rapidly, even climbing up rocks and other areas of the koi pond.

It is important to plant the proper type of vegetation to prevent overcrowding when they become mature. A good example is two common pond plants, Papyrus and Horse Tail (Equisetum fluviatale ). Both of these plants need to be contained, either in a planter pot or a separate pocket built right into the koi pond or waterfall.

Consider creating a bog pond or bog planter on the perimeter of your koi pond. A bog pond is a raised, shallow (6 to 8 inches deep) pond filled with bog plants. Here is one of the best lists I have found to date with more information on the subject. Flood this area with a portion of the unfiltered waterfall return water and allow it to trail back into the koi pond. You have now created a very effective natural biological filter. The fish waste, as it is absorbed by the bog soil, is broken down into ammonia by aerobic bacteria (using oxygen). These aerobic bacteria reproduce at higher rates than do the beneficial Nitrosomonas bacteria, which actually break down the ammonia. So aerobic bacteria compete for oxygen with the Nitrosomonas and use so much of it that the area they inhabit becomes anaerobic, or oxygen-deficient.

The ammonia by-product of fish waste being broken down by aerobic bacteria is now “attacked” by Nitrosomonas. This further breaks it down into toxic nitrite. Then the nitrite is broken down by other aerobic bacteria called nitrobacters, which convert nitrite into beneficial nitrates in the form of food for the plants.

Smaller bog planters can be created at the koi pond’s edge, in much the same way as the larger bog pond was. As the water passes through these bog planters and goes through the process of being cleaned, it picks up oxygen before returning to the pond.  Happy koi, peace and joy!

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