Ammonia and Nitrates in Pools: Understanding How These Chemical Compounds Affect Water Chemistry

Heavy bather loads with excessive waste, large amounts of organic debris, storms, and algae are the primary culprits to high nitrate levels in pools.

Ammonia is a colorless, strongly alkaline gas with a very familiar pungent odor. In fact, it was 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 of this gas on earth. Ammonia takes its name from the Egyptian deity Ammon because a very early discovery of ammonium salts were 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, which 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 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 pools contain ammonia in one form or another.

Sources of ammonia in pools

Ammonia enters the atmosphere from agriculture, automobiles, 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 microns in size or about one-third the width of a human hair. An excess of these particles deposit back to earth primarily in rain 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 in the pool.

Beneficial ammonia

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, which splits 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 monochloramines, which then reacts with free chlorine to from dichloramines. Dichloramine is unstable and rapidly decomposes. Its nitrogen content oxidizes to elemental nitrogen gas and is released into the atmosphere. Quaternary algaecides cause foaming. Poly-quaternary algaecides have a cationic (positive charged) polymer added. The poly-quats do not foam, but they will also 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 monochloramines, which are very effective against yellow algae, as well as clearing up green pools. After this treatment, the pool is super-chlorinated a second time to break up and remove the inorganic chloramines.

Some in the pool industry are of the opinion that the use of these ammonia-based products is problematic. The reason for this is the erroneous belief they will leave ammonia in the water. In fact, nothing could be further from the truth. Is ammonia left behind in the pool from the use of an ammonium salt? Would even adding straight ammonium hydroxide result in ammonia in the pool? The answer is no. This is because of the chemical reaction in pool water where ammonia quickly combines with chlorine to form inorganic chloramines. Ammonia ceases to exist once it reacts and combines with chlorine. The destruction of inorganic chloramines occurs in sufficient levels of free available chlorine (FAC).

Real contaminants

Atmospheric nitrogen from storms converts to nitrates in the pool via the nitrogen cycle. Waste from swimmers such as perspiration and urine that contains urea are the primary sources of detrimental nitrates.

The average adult secretes up to 30 ml (1 oz) of dilute urea daily in his/her urine. Urea in urine contributes 85 percent of total nitrogen. Urea is a nutrient for bacteria and algae and 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 and, as a result, are especially problematic in indoor pools as they 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 470 ml (16 oz) of perspiration per hour. Pool operators may be able to stop people from peeing in the pool, but they cannot stop bathers from sweating. Other sources of nitrates can be from wild animals, such as bears and birds. Improper maintenance and lack of oxidation will lead to high chloramine levels.

When chlorine and ammonia meet

In pools, there are two categories of chloramines present in the water: inorganic chloramines (chlorine combined with nitrogenous ammonia) and organic chloramines (chlorine combined with organic nitrogen waste).

Inorganic chloramines

Inorganic chloramines are a quick reaction of chlorine with ammonia. As 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. It will last from the water station through the pipes and to the faucet. This often results in 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; however, in 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. Those living in areas where this method of water treatment is being used should test their water to determine the chloramine levels. Once the level is determined, increasing the free chlorine level can help to reduce the added chloramines.

Organic chloramines

Organic chloramines from chlorine combined with organic nitrogen are more difficult to break apart then those that are inorganic, as 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 draining the water and dilution.

One might wonder how they can tell whether they have inorganic or organic bound chloramines in their pool water since there is no test to determine the difference. There is a work around, however. After performing additional chlorination or raising free chlorine, re-test the total and free chlorine levels. Any combined numbers that remain after this are organic chloramines.

Draining, dilution, and additional shocking will remove the organic chloramines. Ozone units or ultraviolet (UV) disinfection systems are two proactive ways to prevent the build-up of combined chloramines in either the inorganic or the organic form by breaking them apart. Ozone is a stronger oxidizer than chlorine, while UV systems act to oxidize the precursors to chloramines. According to the Model Aquatic Health Code (MAHC), both act as secondary disinfectant systems.

Inorganic chloramine reactions

As mentioned earlier, ammonia is one nitrogen atom and three hydrogen atoms (NH3). Therefore, when ammonia enters water, three types of inorganic chloramine reactions can occur:

Mono-chloramines form when the ammonia molecule gives up one hydrogen atom for one chlorine atom (NH2Cl + H2O).

  1. Di-chloramines form when ammonia gives up two hydrogen atoms for two chlorine atoms (NHCl2 + H2O).
  2. Tri-chloramines form when ammonia gives up all three hydrogen atoms for chlorine atoms (NCl3 +d H2O).
  3. Mono-chloramines can lead to some minor eye irritation to swimmers, while di-chloramines will cause eye irritation and leave a strong chlorine odor in the air. On the other hand, tri-chloramines are very harmful. Also known as tri-halo methane or nitrogen trichloride, tri-chloramines can cause severe lung and breathing problems and are carcinogens. Nitrogen trichloride is formed when swimmers pee or perspire in the pool.

The pro-active 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 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. 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 the 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 no one would be able to breathe. That said, while nitrogen is more abundant it also is more difficult to distribute into the environment. Humans, as well as animals, need nitrogen for the synthesis of proteins and in the form of nitric acid for proper blood flow. Nitrates are also a primary ingredient in fertilizers for food production and is key to the production of gunpowder.

First, some history. Near the beginning of the First World War, the world was on the brink of food shortages and the availability of gunpowder was also scarce. This was until German scientist 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 then returns to the atmosphere. This is the nitrogen cycle.

Nitrogen ends up in 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 (a common bacteria found all over the world in soil, water, and plants).

Pollen can distribute nitrogen into pools, too. Excessive blue-green algae in pools contains cyanobacteria, 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 groundwater; therefore, it is important to test for nitrates before filling a pool with well water. The recommended maximum level for nitrates in drinking water is 10 parts per million (ppm). This also applies to pools although some industry experts say 10 to 25 ppm is allowable. High levels of nitrates do not pose a health threat to adults; however, consumption of nitrates by infants and toddlers can lead to hemoglobin or ‘blue baby syndrome.’ This condition is a result of a lack of sufficient oxygen to the red blood cells.

Understanding the effects of nitrates

The existence of nitrates in pool water are what causes the majority of quality issues. Ninety percent of ammonia in pools oxidizes to nitrogen then releases back into the atmosphere. For this reason, there can never be a residual of ammonia in pool water. The nitrogen produced by the entrance of ammonia into pools releases quickly as a gas. Heavy bather loads with excessive waste, large amounts of organic debris, storms, and algae are the primary culprits to high nitrate levels in pools.

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 afterwards can help keep them at bay. Dealing with algae quickly will also reduce their formation. Nitrate levels higher than 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 in a pool is by draining and dilution. Diligence in maintenance and pro-active oxidation also helps prevent the cause of nitrates. After heavy bather loads, storms, application of fertilizers in proximity of the pool or any other unusual contamination event, the pool should be immediately oxidized. Enzymes can also be used to treat or eradicate excessive organic debris from leaves, grass, or pollen, while clarifiers can help remove nitrogen containing particulate from filters. Regular backwashing and filter cleaning will also help to keep bacteria and nitrogenous materials from forming inside the tank.

This article was written by Terry Arko and originally appeared on Pool & Spa Marketing [link].