The Nitrogen Cycle

Introduction:

One of the most confusing and intimidating aspects of pond keeping is the science of water quality which includes understanding the nitrogen cycling. You may have heard about nightmares having to constantly monitoring pond water to keep fish healthy. Unfortunately, these stories unnecessarily scare people away from the rewarding hobby of fishkeeping. While pond water quality is important to the health of your fish, it doesn't have to be difficult or confusing. You don't have to obsessed with testing the water quality, constantly adding chemicals and making sure the water is clean and perfectly balanced. It is very possible to adjust your water chemistry too frequently or quickly. Keep it simple and remember that anything worth doing should be done slowly when adjusting water parameters. Let's look at the basic water cycle in a pond and how it can affect fish.

Importance of the Nitrogen Cycle

Nitrogen cycling is a natural process in which various beneficial bacteria break down compounds such as ammonia and nitrite and reduce them to less harmful compounds such as nitrate. This process takes place in three stages, from ammonia to nitrite and the final conversion to nitrate. The accumulation of ammonia is the first step starting the nitrogen cycle. This typically comes from the decomposition of introduced fish waste and other organic inputs. As ammonia increases, nitrosomonas bacteria begin to consume it and break it down into nitrites. When nitrite begins to accumulate, denitrifying bacteria break it down into nitrates. Nitrates are then removed from the system by absorption of plants, algae growth, or removed via water changes. Because there are so many biological processes involved, it usually takes three to six weeks for a pond system to complete a full cycle.

Balancing Pond Ecosystems

Ammonia

Ammonia is the main byproduct of fish and acts as the start of the natural cycle. Ammonia is partly excreted by the kidneys of the fish, but mainly through the gills. This is important because it reminds us that when a fish's gills are damaged, the fish suffer more than just breathing problems. They may also have trouble getting rid of ammonia. A high ammonia concentration indicates that the pond does not yet have enough beneficial nitrogen-reducing bacteria. These bacteria multiply over time, so ammonia problems are most common during the first six to eight weeks of the pond's inflow. Later on, ammonia levels can rise again when the filter becomes clogged or from changes such as fish loss or adding more to the bio-load. This is when organic compounds begin to rot in the pond. As ammonia rises, you may see your fish "jump" out of the pond due to tissue damage caused by concentrated ammonia exposure. Ammonia control includes reducing or stopping fish feeding, feeding a lower protein diet (<30%) and/or improving pond filtration. While water changes are the best remedy for ammonia build-up that threatens your fish, you can also use an ammonia neutralizer/remover to temporarily provide relief. Once the source of the ammonia is corrected the neutralizer and additional water changes may be discontinued.

Nitrite Exposure

Nitrite is produced from ammonia in the water by beneficial nitrogen-reducing bacteria. These bacteria break down hydrogen ions from ammonia and replace them with oxygen. The pH of the water then drops as these hydrogen ions are released. Your fish will absorb nitrites through their skin and gills. Inside the fish, nitrites bind red blood cells and turn them from red to brown. Brown blood disease is caused by the accumulation of nitrites in the system. Nitrites are toxic at concentrations as low as 0.1 ppm, and fish that are lost from nitrite poisoning usually have distended gills.

Nitrate is Safer

Nitrate is an end product of the nitrogen cycle. Nitrites are broken down by other beneficial nitrogen-reducing bacteria and converted to nitrates as a result of this bacterial conversion. Plants and algae use nitrates as well as phosphates and iron for cell growth. When the nitrogen cycle is complete, you may see a sudden algae bloom or an explosion of green water at the bottom of the pond, obscuring your view of the fish. This end of the nitrogen cycle is usually not a problem for fish health, as fish are not harmed by acute or sudden exposure. However, with chronically high nitrate levels, you may notice weaker fish, slower growth and an overall increase in disease. This is because high nitrate levels mean poorer water quality, which causes stress, making fish more susceptible to disease and parasites. Nitrates should always be below 75 ppm for a healthy pond with koi. You can add plants, do water changes, or encourage algae growth to reduce nitrates. The emerald green algae at the bottom of the pond has tremendous health benefits, the biggest of which is nutrition for the fish. That's why we always say a little green in your pond is a good thing.

Aquatic Organisms and Cycling

Testing the pH of your pond water pH testing is simply the measurement of free hydrogen ions (H) in a pond. It is measured on a scale of one to fourteen, anything below seven is acidic and anything above seven is alkaline. The pH required for aquatic organisms is between 5.5 and 8.0. Koi and goldfish can tolerate very high pH readings.

Some pond owners spend a lot of time lowering the pH, but this is not necessary unless the pond also has ammonia. Ammonia toxicity is affected by pH, so ammonia is more toxic at higher pH values. Below pH 7.2, most of the ammonia is ionized to ammonium and is much less toxic. The pH level of ponds affects fish in several ways. First, if it is too low, the result is a disease inside the fish called acidosis. Symptoms include loss of appetite and then the formation of excess mucus, as well as isolation and resting at the bottom of the pond. This is followed by fin and body veining (red streaks) and possibly loss of the fish. If the pH is too high (above 10.0), the fish will produce extra mucus and start pumping at the surface of the water. This condition, called alkalosis, is difficult to correct quickly once it occurs.

pH Testing

Water testing for pH is simply the measurement of free hydrogen ions (H) in a pond. It is measured on a scale of one to fourteen, anything below seven is acidic and anything above seven is alkaline. The pH required for aquatic organisms is between 5.5 and 8.0. Koi and goldfish can tolerate very high pH readings. Some pond owners spend a lot of time lowering the pH, but this is not necessary unless the pond also has ammonia. Ammonia toxicity is affected by pH, so ammonia is more toxic at higher pH values. Below pH 7.2, most of the ammonia is ionized to ammonium and is much less toxic.

The pH level of ponds affects fish in several ways. If it is too low, the result is a disease inside the fish called acidosis. Symptoms include loss of appetite and then the formation of excess mucus, as well as isolation and resting at the bottom of the pond. This is followed by fin and body veining (red streaks) and possibly loss of the fish. If the pH is too high (above 10.0), the fish will produce extra mucus and start pumping at the surface of the water. This condition, called alkalosis, is difficult to correct quickly once it occurs.

Understanding Chlorine and Chloramine

Municipal water supplies often have chlorine and chloramines in tap water to make it drinkable. However, these same compounds are dangerous and hazardous to fish and other living organisms. It can kill them if exposed at even small concentrations for an extended period of time. Basically, these compounds damage and destroy the gills of fish. Dechlorinators such as the prime or pond water conditioner remove and neutralize these compounds and should be used whenever more than 5 to 10 percent of the total pond water volume is added.

Conclusion

The only way to know for sure what is wrong with your pond is to test the water for harmful compounds or shifting parameters. However, there is no need to do regular testing, especially if your stocking levels are kept low. We recommend stocking your pond with half of the maximum bioload your filtration can handle. If you notice that your fish are behaving different, you can test the water. Yellowing or die-back of aquatics plants and alagae could be a first indication that a test is needed. With a simple test kit, you can determine quickly the next steps to promote a healthy environment for your fishy friends. Although, it may seem intimidating at first, once you understand how to measure and control pond water parameters, it will be easy and easier. Most importantly, high quality water leads to happy and healthy fish.