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Ammonia and Nitrates in Swimming Pools

By Terry Arko


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.