The Nitrogen Cycle Explained

A well-balanced and healthy ecosystem in a pond is the ideal environment for aquatic plants and fish to thrive. Building and maintaining this ecosystem is simple once you have a good grasp of the basics. In this article, we will go over the nitrogen cycle and why it is vital to all aquatic life in a pond.

Nitrogen Cycle Basics

The nitrogen cycle in a Koi pond is the biological filtration system that maintains safe levels to support aquatic life such as fish and plants. Without an established ecosystem, levels of nitrites and ammonia will become elevated putting your fish in danger.

Once a pond is built, nitrogen from the atmosphere penetrates the water through rainfall, runoff and wind. Branches, leaves and other debris will also infiltrate the pond. Waste from fish and uneaten fish food in mature Koi fish ponds will also contribute to the debris, and overtime it will begin to decay with the assistance of beneficial bacteria or microorganisms known as Nitrosomonas and Nitrobacter.

Ammonia is released in the water while the debris breaks down. Nitrosomonas consume ammonia and oxygen in the water and they produce nitrites. Nitrites are harmful to Koi as well, so another organism known as Nitrobacter will lower the nitrites in the pond and turn them into harmless nitrates. Then the nitrates are reduced by changes of the water or consumed by aquatic plants and algae.

New Pond = New Bactria

Establishing a healthy population of good bacteria, Nitrosomonas and Nitrobacter takes time. So if you just built a pond, you may wish to wait four to six weeks before you add fish, otherwise the ammonia and nitrites levels will be too high. Try adding beneficial bacteria to your pond and boost dissolved oxygen levels with an aeration system.

Maintain Bacteria Levels

At the beginning of spring when mature ponds are waking up after a cold winter, a similar cycling process happen. Some Nitrosomonas and Nitrobacter will survive in the gravel and filtration media and begin to take over but giving them a boost is a good idea.

Choose one that is formulated for use in cooler temperatures. This will make it perfect for early spring applications. These microorganisms live in your filtration media, so only wash it if water flow becomes restricted.

Cycled and Ready for Fish

For the safety of your fish, prepare your water before you add them. During the first four to six weeks, monitor ammonia and nitrite levels using a test kit. Once your test results indicate that your levels are safe, your pond is ready for fish. Start out by adding only a few small fish at the beginning to see how well they do before you add more.

Pro Tip: Keep in mind that as your fish grow, they produce more waste. A good rule of thumb to help keep your water safe is to have no more than one inch of fish per square foot of surface area.