Combat Rust and Corrosion… Indoor Pool and Spa

Measures to combat Rust and Corrosion in Indoor Pool and Spa Facilities

Indoor commercial swimming pools and spas indeed face unique challenges when it comes to rust and corrosion of building internals.

Causes of Rust and Corrosion

Liquid Chlorine Use

The employment of liquid chlorine in pool maintenance can contribute to corrosion. The off-gassing of chlorine, coupled with the processes involved in its handling and manual dosing, can exacerbate corrosive conditions in the surrounding environment.

Hydrochloric Acid Fuming

A significant contributor to building corrosion, particularly in indoor pool environments. The use of hydrochloric acid for pool water pH control leads to visible fuming in humid conditions, causing severe corrosion, especially in indoor plant rooms.

Improperly Balanced Water

One of the less obvious but equally significant causes of rust and corrosion in indoor pool environments is water that is not correctly balanced. The chemistry of pool water plays a crucial role in the maintenance of the facility. Imbalances in pH, chlorine levels, and other chemical components can lead to accelerated corrosion of both the pool infrastructure and the surrounding structures.


These are by-products of the reaction between chlorine (used for pool and spa sanitation) and organic waste products in the water. Chloramines are corrosive and can be present in both liquid and gaseous states.

Inadequate Plant Room Ventilation

A significant factor contributing to rust and corrosion in indoor pool environments is inadequate ventilation in plant rooms. These areas, where pool chemicals are stored and managed, are particularly susceptible to the buildup of chemical fumes. Without proper ventilation, these elements accumulate and create a corrosive environment. This not only affects the equipment and infrastructure within the plant room but can also have a wider impact on the overall structural integrity of the facility.


Warm, moisture-saturated air leads to condensation on cooler surfaces. This moisture often has a low pH and contains salts and chloramines, contributing significantly to corrosion, particularly on metal surfaces.

Solutions to Minimise Rust and Corrosion

Onsite Chlorine Generation (OCG)

Implementing an onsite chlorine generation system is an effective strategy to mitigate corrosion risks. By managing the chlorination process directly on the premises, it eliminates the need for handling and using liquid chlorine. This method not only simplifies the maintenance process but also significantly reduces the corrosive effects associated with liquid chlorine. Additionally, maintaining low salt levels in the system further contributes to reducing the overall corrosive environment in indoor pool and spa facilities.

Use of Carbon Dioxide for pH Control

Replacing hydrochloric acid with carbon dioxide for pH control is an effective method to prevent fuming. This approach necessitates implementing additional safety measures, such as atmospheric monitoring for CO2 leaks, to ensure a safe environment in plant rooms.

In cases where using carbon dioxide is not feasible, an alternative strategy involves the use of low fuming hydrochloric acid coupled with the installation of HCL Vapor Scrubbers on the hydrochloric acid storage tanks. This combination helps to reduce the risk of corrosive fumes, thereby offering a safer and less corrosive environment.

Water Chemistry Analysers and Controllers

To address the challenge of maintaining correctly balanced pool water, commercial chemical analysers/controllers (measuring FAC, TCL pH & ORP) offer a sophisticated solution. Utilising state-of-the-art technology, these systems continuously monitor and balance swimming pool water quality. They function by combining the precision of laboratory testing with real-time online monitoring and control capabilities. By doing so, they ensure that the chemical composition of the pool water is maintained within optimal ranges, thereby minimising the risk of corrosion. These controllers are instrumental in reducing the need for excessive chemicals, which can be a contributing factor to corrosion, ensuring a healthier and more sustainable indoor pool environment.

Advanced Oxidation Process (AOP) Systems

AOP systems are a cutting-edge solution in the management of pool water quality, particularly effective in addressing the challenge of chloramines in indoor pool environments. These systems function by continuously breaking down chloramines, thereby preventing their accumulation in the water and the surrounding air.

Chloramines, which are a byproduct of chlorine interacting with organic matter in the pool, are known for their corrosive properties, especially in enclosed spaces. By effectively reducing the level of chloramines, AOP systems play a crucial role in protecting the structural integrity of indoor pool facilities. In addition to effectively reducing chloramine levels, a critical advantage of AOP systems is their ability to oxidize trihalomethanes (THMs). THMs are another byproduct of chlorine treatment and a major contributor to corrosion, particularly in indoor environments. While typical UV systems may not adequately address THMs, AOP systems excel in this regard, further safeguarding the structural integrity of indoor pool facilities.

By minimising the levels of both chloramines and THMs, AOP systems significantly enhance air quality, creating a more enjoyable and healthier environment for users. This also substantially contributes to the longevity of the facility by reducing corrosive damage often linked with traditional chlorination methods.

The implementation of AOP systems is thus seen as a proactive and technologically advanced approach to maintaining both the aesthetic and structural aspects of indoor swimming pools and spas.

Plant Room Ventilation

It is essential to ensure that the plant room is adequately ventilated. This can be achieved by using appropriate mechanical exhaust fans, specifically chosen based on the dimensions and specific requirements of the plant room. Such ventilation strategies help in mitigating the buildup of moisture, chemical fumes and consequently, reduce the risk of corrosion.

Improved Air Handling

The installation of effective air handling systems throughout the facility plays a crucial role in managing indoor environments. These systems are designed to remove moisture from the air and facilitate the exchange with fresh air. By doing so, they significantly reduce the occurrence of condensation, which is a major contributor to corrosion.

Additional Measures

Use of Corrosion-Resistant Materials

Constructing or retrofitting with materials that are resistant to corrosion (like stainless steel, certain plastics, or treated metals) can be beneficial.

Regular Maintenance and Inspections

Regularly inspecting and maintaining pool and spa equipment and building internals can help catch and address corrosion issues early.

Environmental Controls

Maintaining optimal temperature and humidity levels inside the pool and spa area can help reduce the risk of condensation.

Protective Coatings

Applying protective coatings to metal surfaces can provide an additional barrier against corrosion.

Water Chemistry Management

Regularly monitoring and adjusting the pool’s water chemistry (pH, chlorine levels, etc.) can reduce corrosive conditions.


In conclusion, while the presence of an indoor pool or spa increases the corrosive potential in a building, implementing a combination of these strategies can significantly minimise the risk and extend the life of the building’s internal structures. Regular monitoring and proactive maintenance are key to managing these challenges effectively.

By Technical Expert
John Morrison

Bachelor of Science degree, double major; Marine Biology, Sustainable Resource Management.

Over 10+ years experience in the aquatic industry, providing advice and training to Councils, Health

Departments and professionals in the industry.

Experience working in both the water testing and water treatment industry.
Research experience in the laboratory as well as out in the field, contributing to research with NSW Fisheries that was later published in scientific journals.

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