Ammonia and Nitrates in Swimming Pools

Ammonia is a colorless, strongly alkaline gas with a very familiar pungent odor. The first complex molecule discovered in space in the galactic dust clouds of the Milky Way, it also makes up the rings of the planet Saturn. Ammonia gas consists of one nitrogen atom and three hydrogen atoms (NH3). Volcanoes and hot springs were the original early sources on our planet. Ammonia takes its name from an Egyptian deity Ammon because of a very early discovery of ammonium salts found in camel dung near the ancient site of his temple.

Ammonia gas is very soluble when mixed in water. It creates an alkaline liquid known as ammonium hydroxide. The liquid ammonium hydroxide is simply household ammonia used for disinfecting and cleaning. This is one of many forms of ammonia produced. Ammonia is in fertilizers, nitric acid, sodium carbonate (soda ash), explosives, nylon and baking soda (sodium bicarbonate).

Two of the most common chemicals for swimming pools and hot tubs are sodium bicarbonate and soda ash. Saturating salt with ammonia and carbon dioxide creates sodium bicarbonate. Heating sodium bicarbonate creates soda ash. Both of these useful pool products start with ammonia. Many cleaners and algaecides for pool use contain ammonia in one form or another.

Ammonia in Swimming Pools

Ammonia enters the atmosphere from agriculture, autos and industry. Ammonia releases into the atmosphere from livestock manure and agricultural fertilizer. When this ammonia gas mixes with atmospheric emissions, it creates microscopic particles. These particles measure about 2.5 micron in size or about one-third the width of a human hair. An excess of these particles deposit back to earth, primarily via precipitation. Somewhere in the process ammonia releases nitrogen, which converts to nitrite, which then converts to nitrate. This explains why nitrates increase in pools after heavy rains. High nitrates will increase the consumption of free available chlorine and cause excess algae growth. Contrary to popular belief, the use of ammonium hydroxide or ammonium-based algae treatments does not leave a residual of ammonia behind in the pool.

There are products that incorporate compounds of ammonia used to remove algae and clean up water. Two products for algae are quaternary ammonium and poly-quaternary ammonia, used to fight against green algae. Both of these products incorporate an ammoniated compound that serves to lower the water surface tension. This causes the algae to take in a toxin splitting the cell wall. When used in well-maintained pools along with recommended levels of free chlorine, ammonia will combine to form inorganic chloramines. The first reaction of ammonia in a chlorinated pool is with hydrogen ions. This quickly forms ammonium ion. The ammonium ion reacts with hypochlorous acid to form mono-chloramines. Monochloramine reacts with free chlorine to from dichloramines. Dichloramine is unstable and rapidly decomposes. Its nitrogen content oxidizes to elemental nitrogen gas and releases in the atmosphere. Quaternary algaecides cause foaming. Poly-quaternary algaecides have a cationic (positive charged) polymer added. The poly-quats do not foam but they also will act as a flocculant and diminish the effectiveness. There are ammonia enhancer products that incorporate the use of ammonium sulfate salt. The salt releases ammonium and sulfate ions in water. Chlorine shock oxidizes the ammonium and free chlorine combines to create mono-chloramines. The chloramines are very effective against yellow algae and green pools. The pool is super-chlorinated a second time in order to break up and remove the inorganic chloramines. Some in the pool industry are of the opinion that use of these ammonia-based products is problematic. The reason for this is the erroneous belief that these products will leave ammonia in the water. Nothing could be further from the truth. Is there ammonia left behind in the pool from use of an ammonium salt? Would even adding straight ammonium hydroxide result in ammonia in the pool? The answer is no. Because of the chemical reaction in swimming pool water, ammonia quickly combines with chlorine to form inorganic chloramines. Ammonia ceases to be once it reacts and combines with chlorine. The destruction of inorganic chloramines occurs in sufficient levels of free available chlorine.

Real Contaminants

Atmospheric nitrogen from storms converts to nitrates in the pool via the nitrogen cycle. Waste from swimmers' perspiration and urine that contains urea are the primary sources of detrimental nitrates. Human adults secrete up to an ounce of dilute urea daily in their urine. Urea in urine contributes 85 percent of total nitrogen. Urea is a nutrient for bacteria and algae. It is also a primary source of ammoniated chloramines. An extreme result of urea and chlorine will be the formation of toxic chloramines such as cyanogen chloride (CNCl) and trichloramine (NCl3). These are both very toxic to breathe. They are especially problematic in indoor pools and can cause lung and eye irritation to swimmers. Peeing in the pool is never a good thing. However, urea is also present in sweat and most active swimmers exude a pint of perspiration per hour. We may be able to stop the pee, but we cannot stop the sweat. Other sources of nitrates can be from wild animals such as bears or ducks and birds. Improper maintenance and lack of oxidation will lead to high chloramine levels.

When Chlorine and Ammonia Meet

In swimming pools, there are two categories of chloramines present in the water. Inorganic chloramines equal chlorine combined with nitrogenous ammonia. Organic chloramines equal chlorine combined with organic nitrogen waste. Inorganic chloramines are a quick reaction of chlorine with ammonia. Because inorganic chloramines hold together longer than free chlorine, many drinking water facilities use chlorine and chemical ammonia to produce chloramines for disinfecting. These inorganic chloramines are more stable and maintain a residual longer than free chlorine. They will last from the water station through the pipes and to the faucet. This causes a strong chloramine smell at the tap. This manufactured form of disinfecting drinking water is chloramination. Inorganic chloramines may be good for treating drinking water but in swimming pools, they are an irritant to swimmers and lead to eye, skin and lung problems. Consumption of free chlorine occurs in the process of oxidation of the chloramines. Most drinking water municipalities will show in their reports if they are practicing chloramination. If your water source is using this method then test the water to determine the level of chloramines. Once the level is determined, increasing the free chlorine level can help to reduce the added chloramines. Organic chloramines from chlorine combined with organic nitrogen are more difficult to break apart then the inorganic. They do not respond to breakpoint chlorination. In fact, it can take many frequent super-chlorination shocks to begin to see any reduction. Another method could be frequent oxidizing with a non-chlorine shock known as potassium monopersulfate (MPS). The easiest and most efficient way to remove organic bound chloramines is by drain and dilution. One might wonder how to tell whether you have inorganic bound chloramines or organic bound chloramines since there is no test to determine the difference. Re-test the total and free chlorine again after performing additional chlorination or raising free chlorine. Any combined numbers that remain after this are organic chloramines. Draining, dilution and additional shocking will remove the organic chloramines. Ozone units or UV are two proactive ways to prevent the buildup of combined chloramines in either the inorganic or the organic form. Ozone is a stronger oxidizer than chlorine and can break apart and prevent the buildup of both inorganic and organic chloramines. UV systems act to oxidize the precursors to chloramines. Both ozone and UV act as secondary disinfectant systems according to the Model Aquatic Health Code (MAHC).

When ammonia enters water three types of inorganic chloramines reactions can occur:

  • Mono-chloramines form when the ammonia molecule gives up one hydrogen atom for one chlorine atom. NH2Cl + H2O.
  • Di-chloramines form when ammonia gives up two hydrogen atoms for two chlorine atoms. NHCl2 + H2O.
  • Tri-chloramines form when ammonia gives up all three hydrogen atoms for chlorine atoms. NCl3 + H2O.

Mono-chloramines can lead to some minor eye irritation to swimmers. Di-chloramines will cause eye irritation and heavy chlorine odor in the air. Tri-chloramines are very harmful. Also known as tri-halo methane or nitrogen trichloride, they can cause severe lung and breathing problems and are carcinogens. Nitrogen trichloride is formed when swimmers pee in the pool, as well as from perspiration.

The proactive practice of proper, regular oxidation can prevent the accumulation of detrimental chloramines. As mentioned previously, MPS, ozone or UV systems can help to prevent the build-up of harmful chloramines.

The Real Problem

Ammonia as we know it does not exist in pool water due to the quick reactions that take place. Products that contain ammonia are not the problem in pools. The real problem is from organic nitrogen when it combines with chlorine to form organic chloramines. As mentioned previously organic chloramines are much more difficult to remove from water and they are a source of toxic air and overwhelming chlorine odor. The main source of stubborn organic chlorine is from organic debris and excessive swimmer waste and not from using ammonia-based products.

The Nitrogen Cycle

Nitrogen makes up 78 percent of our atmosphere. Easily assimilated through our breathing, oxygen makes up 22 percent of the atmosphere. If it were not for oxygen, fire would not burn and we would all suffocate. Therefore, we can all be grateful.

While nitrogen is more abundant, it also is more difficult to distribute into the environment. Humans and animals need nitrogen for the synthesis of proteins and in the form of nitric acid for proper blood flow. Nitrates are a primary ingredient in fertilizers for food production. They are also key to the production of gunpowder. Near the beginning of WWI, the world was on the brink of food shortages and there was a shortage of gunpowder. A German scientist named Fritz Haber discovered a method for creating ammonia by synthesizing it from atmospheric nitrogen. His process of nitrification of ammonia proved successful and there was enough nitrate derived to grow the world's food and to fight its battles. Fixation is the process that releases nitrogen from the atmosphere by lightning strikes or bacteria in soil. The nitrifying process starts when nitrogen in air pockets of the soil fix to bacteria. Further reaction of bacteria with nitrogen leads to ammonia. Ammonia is broken down further into nitrite and then finally as nitrates. In soil and certain plants denitrifying bacteria converts nitrates back into nitrogen. The released nitrogen goes back into the atmosphere. This is the nitrogen cycle.

Nitrogen ends up in swimming pools from storms, via human or animal waste and algae growth. Poor disinfection, algae or lots of organic debris will increase nitrates. Replication of the nitrogen cycle takes place in poorly maintained pools by certain nitrifying bacteria like pseudomonas. Pollen can distribute nitrogen into pools. Excessive blue-green algae in pools contains cyano-bacteria which is nitrogen fixing. Green pools take more nitrogen from the atmosphere and nitrification leads to more nitrates. In farm areas, nitrates are present in the groundwater.

There are tests available for nitrates. Test for nitrates before filling a pool with well water. The recommended maximum level for nitrates in drinking water is 10 ppm. This applies to swimming pools although some state that 10 to 25 ppm is allowable. High levels of nitrates do not pose a health threat to adults. However, in infants to toddler age consumption of nitrates can lead to hemoglobin or "blue baby syndrome," a condition that causes a lack of sufficient oxygen to the red blood cells.

Understanding the Effects of Nitrates

The most abundant form of nitrogen in pools is not from ammonia but rather from nitrates. Ninety percent of ammonia in pools oxidizes to nitrogen then releases back into the atmosphere. Heavy swimmer loads with excessive waste, large amounts of organic debris and algae in pools are the primary culprits to high nitrate levels. In short, a well-maintained pool free of organic debris with routinely performed practical oxidation will not experience problems from nitrates. While storms bring in nitrates, immediate shocking afterward can keep them at bay. Dealing with algae quickly also helps reduce the mechanism for the formation of nitrates. Nitrates at levels above 25 ppm can lead to rapid decomposition of free chlorine and excessive algae problems.

Removing Nitrates from Pool Water

The most practical and cost-effective way to reduce nitrate levels is by draining and dilution. Diligence in maintenance and proactive oxidation help prevent the causes of nitrates. Installation of secondary oxidation units like ozone and UV may be effective at prevention. Apply immediate oxidation after heavy swimmer loads, storms, application of fertilizers in proximity of the pool or any unusual contamination event. Remove or treat excessive organic debris from leaves, grass or pollen. An enzyme can help to break pollen down quickly. Clarifiers can help in faster removal of nitrogen containing particulate to the filters. Regular backwashing and cleaning of filters helps by keeping bacteria and nitrogenous materials from forming inside the tank.


  • Ammonia as we know it does not exist in pool water because it reacts with hydrogen ions to from ammonium ions.
  • Ammonium ions oxidize rapidly by proper free available chlorine.
  • Ammonia-based specialty chemicals will not cause poor water quality.
  • Organic nitrogen compounds (organic chloramines) are the real problem in pools because they oxidize at a much slower rate than ammonia bound chloramines (inorganic chloramines).
  • Ammonia contributes less than 10 percent of nitrates in pools.
  • Poorly maintained pools with persistent organic debris and algae will cause increased nitrates. Wild animals, ducks and birds can bring nitrates in through waste.
  • Nitrates can increase in pools immediately after a storm.
  • Urine and perspiration in reaction with insufficient free available chlorine are primarily responsible for toxic chloramines and increased nitrates.
  • Proactive oxidation and proper maintenance can help to prevent the increase of nitrates.
  • Test groundwater in agricultural areas for nitrates before filling pools.



Terry Arko has more than 30 years of experience in the pool and spa/hot tub industry, working in service, repair, retail sales, chemical manufacturing, customer service, sales and product development. A certified pool operator (CPO) and CPO instructor through the National Swimming Pool Foundation (NSPF), Arko is currently a water specialist for NC Brands, parent company of SeaKlear and Natural Chemistry, which is a manufacturer of pool and spa products. For more information, visit