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  • Writer's pictureJefferson Landscape

The Nitrogen Cycle of Your Pond

The nitrogen cycle may be one of the most important cycles on earth because it’s the building block of all organic life forms. This is an important cycle to know and understand because it can help answer a lot of questions that you might have regarding fish health and water quality.

The Process

The nitrification process or nitrogen cycle is a biological process that changes ammonia to nitrite and then to nitrate. The amazing part of this cycle is it can start at multiple points and has the ability to go backward and forward in the cycle, allowing for a variety of complex biological processes to occur.

Unfortunately, the nitrogen cycle makes most of us scratch our heads, so it’s our goal to help you understand this critical, biological process. But be careful, a little knowledge goes a long way, and putting it into action can sometimes do harm to your pond. We’ve seen new pond owners worry about the many forms of nitrogen in the pond who begin altering the water chemistry in hopes of creating the perfect aquatic environment. If the pond is designed and built properly and you clean the debris out of your skimmer on a regular basis, add bacteria, and trim dead aquatic plants you’ll have no problems and you will have allowed this complex cycle to hum along as it was designed to—in perfect balance.

Here are Nitrate Producers and the Nitrate Eater, as well as

the Ammonia Producers and Ammonia Eaters

Nitrate Producers

Lightning Storms

Nitrates can be added to your pond by way of atmospheric fixation. This occurs during lightning storms when nitrogen gas is broken up., allowing it to combine with oxygen-forming nitrogen oxide which is dissolved in rainwater. This is why our lawns become so green following a lightning storm—it not only receives water, but also a burst of nitrate (fertilizer). This is also why ponds can turn murky or have an algae bloom after a storm with charged particles. If you add some liquid bacteria immediately after the storm, you can counteract the influx of nutrients.

The Air, The Rain, The Pond

Basic nitrogen gas makes up approximately 78% of our atmosphere. This form of nitrogen is inert and cannot be used by plants and animals. It makes its way into the pond via the rainwater and takes a great deal of energy to convert it to a form that is usable to plants. Nitrogen gas returns to the atmosphere when it leaves the pond through the evaporation of pond water.

Nitrate Eater

Aquatic Plants

Nitrate is either absorbed by aquatic plants or, in anaerobic conditions, it goes through the process of de-nitrification, which changes the nitrate back to nitrogen gas. Although uncommon, nitrate can also be removed by water changes if unusually high levels are detected in the water.

Ammonia Producers

Fertilizer Runoff

Be conscious of the amount of fertilizer you use around your pond (using organic fertilizers is best – see our blog Organic Fertilizers). During a heavy rain or over-irrigation, the fertilizer, which is made of ammonia and phosphorus, could wash into your pond creating an algae bloom, water quality problem, or even kill your fish.

Fish Food and the Resulting Waste

Most of our ponds have fish in them. When the fish are fed (koi – goldfish won’t need to be fed once the pond is established), the results is a combination of un-eaten fish food and fish waste. Both contribute to the ammonia level in the pond. Don’t feed your fish more than they can eat in five minutes. This will save money by not wasting food, but it will also help keep your water healthy.

Dead Plant and Animal Debris

Organic debris, like leaves, lawn clippings, and dead fish or insects will break down, forming ammonia as a byproduct, starting the cycle of de-nitrification again. Reduce the amount of plant debris in your pond by using a skimmer filtration system.

Ammonia Eaters


The waterfall in your pond creates oxygen necessary for efficient nitrification. This oxygen is also necessary for the survival of your fish.

Ammonia Nitrification

The large amount of surface area both on the surface of the biological filter media (in your waterfall and skimmer), as well as the rocks and gravel inside the pond allows for the colonization of beneficial bacteria that are responsible for the nitrification process, changing ammonia to less toxic forms of nitrite and the usable form of nitrate.

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