Why Ammonia Nitrogen Rises in Pool Water

Elevated ammonia nitrogen in a swimming pool is usually a sign that contamination is entering the water faster than disinfection and circulation can remove it. Ammonia itself is not the only concern; it reacts with chlorine to form chloramines, which cause the characteristic “pool smell,” eye and skin irritation, and reduced disinfection efficiency.

The main source is bathers. Sweat, urine, saliva, skin cells, cosmetics, and sunscreen all introduce nitrogenous compounds. Urea from urine can break down into ammonia, especially when the pool is heavily used and free chlorine is not maintained at an adequate level. Children’s pools and training pools often show higher ammonia loads because of frequent use and accidental urination. Bathers who do not shower before entering the pool increase the problem.

Source water can also contribute. If the fill water or make-up water contains ammonia, it will accumulate in the pool unless it is removed by oxidation or dilution. This is more common when the water supply comes from surface water or a secondary supply system.

Poor water management is another major factor. If circulation and filtration are inadequate, ammonia is not distributed to the disinfection zone or removed by the filter. Dirty filters, clogged media, short circulation times, and insufficient fresh water replacement allow ammonia to build up. High pH and warm water can also reduce the oxidizing power of chlorine, slowing ammonia removal.

Disinfection practice matters greatly. When free chlorine is too low, ammonia is not fully oxidized and chloramines form. When cyanuric acid is overused, chlorine becomes less effective and ammonia may persist. On the other hand, a sudden heavy chlorine dose without proper monitoring can create strong irritants before the ammonia is destroyed. Testing errors, reagent aging, turbidity, and residual chlorine interference can also produce falsely high ammonia readings.

The consequences are practical. Chloramines irritate the eyes, skin, and respiratory tract. They also indicate that the pool is not properly sanitized, increasing the risk of microbial contamination. Ammonia can promote algae growth and cloudiness, and it consumes chlorine, raising operating costs.

To correct the problem, start with source control: require showering before swimming, prohibit urination in the pool, and manage bather load. Improve circulation and filtration, backwash or replace filter media as needed, and increase fresh water replacement. For chemical control, breakpoint chlorination is the standard method: add enough chlorine to oxidize ammonia and chloramines completely, while monitoring free chlorine, combined chlorine, pH, and ORP. Ozone, UV, or activated carbon can provide additional support. If the fill water is high in ammonia, pretreat it before use.

In short, high ammonia nitrogen in a pool is not a single fault but a signal of combined contamination, insufficient oxidation, and inadequate water exchange. Regular testing and proper operation are essential to keep ammonia and chloramines under control.