PWTAG Standards and ChloroKlean: Approved Chemistry with Added Protection

What is PWTAG and why does it matter?

The Pool Water Treatment Advisory Group (PWTAG) is the UK's leading independent authority on pool water treatment standards. Through two key publications - the Code of Practice and the book Swimming Pool Water: Treatment and Quality Standards for Pools and Spas (now in its third edition) - PWTAG sets the benchmark for how pools, spas, and hydrotherapy facilities manage water quality.

PWTAG guidance carries significant weight because the HSE recognises it as a useful resource for pool operators when drawing up their operating procedures. Enforcing authorities - both HSE and local authorities - consider PWTAG guidance as the standard to be achieved in effectively managed swimming pools. Non-compliance may be taken into account when assessing whether appropriate standards have been met.

For pool operators, hydrotherapy centres, and leisure facility managers, understanding where your water treatment chemistry sits within the PWTAG framework is not optional - it is a core part of demonstrating competent water management.

PWTAG's approved primary disinfectants

PWTAG's Code of Practice is clear about which chemicals are approved for primary pool disinfection. The recognised primary disinfectants are all chlorine-based:

• Sodium hypochlorite (liquid chlorine)
• Calcium hypochlorite (granular or tablet form)
• Sodium dichloroisocyanurate (stabilised chlorine)

These inorganic chlorine-based disinfectants are the foundation of PWTAG's approach to pool water treatment. The framework is built around maintaining a measurable free chlorine residual in the pool water as the primary barrier against waterborne pathogens.

This is where ChloroKlean's formulation becomes directly relevant.

ChloroKlean: PWTAG-approved chemistry at its core

ChloroKlean is a blend of sodium hypochlorite and sodium chlorite that activates in situ to generate chlorine dioxide. The critical point is this: sodium hypochlorite - ChloroKlean's base component - is explicitly listed on PWTAG's approved primary disinfectant list.

This means a pool or hydrotherapy centre using ChloroKlean is not stepping outside PWTAG's approved chemistry. The primary disinfection is delivered by sodium hypochlorite - exactly what PWTAG recommends. The sodium chlorite component reacts with the sodium hypochlorite to generate chlorine dioxide in situ, providing additional capabilities that address challenges PWTAG's own guidance identifies as critical.

"Pool operators sometimes think chlorine dioxide means moving away from PWTAG-approved chemistry. The reality is the opposite. ChloroKlean's sodium hypochlorite base is one of the primary disinfectants PWTAG recommends. The in-situ chlorine dioxide generation gives operators more than PWTAG compliance - it gives them better water quality outcomes." - Gavin Owen, Managing Director, ChloroKlean

The challenges PWTAG identifies - and how chlorine dioxide addresses them

PWTAG's guidance does not just list approved chemicals. It also identifies the key challenges that pool operators face in maintaining safe, compliant water quality. Several of these challenges are precisely where the in-situ chlorine dioxide generation in ChloroKlean provides measurable advantages.

Biofilm

PWTAG recognises biofilm as a significant threat to pool water quality. Biofilm is the slimy layer of microorganisms that forms on pool surfaces, inside pipework, in balance tanks, and on filtration equipment. Once established, biofilm harbours pathogens including Pseudomonas aeruginosa and Legionella species, protecting them from the free chlorine residual in the bulk water.

Standard chlorine-based disinfectants - including sodium hypochlorite on its own - cannot penetrate the extracellular polymeric substances (EPS) that hold biofilm together. They kill bacteria in the open water but leave the biofilm reservoir intact, which is why some pools experience persistent or recurring bacteriological failures despite maintaining correct free chlorine levels.

Chlorine dioxide actively penetrates and breaks down biofilm. When ChloroKlean generates chlorine dioxide in situ, it attacks the biofilm matrix itself, eliminating the bacterial colonies at source rather than simply treating the planktonic bacteria they release into the water.

Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most commonly detected problem organisms in pool water testing. PWTAG and CHA (Canine Hydrotherapy Association) standards both require regular bacteriological testing for Pseudomonas, and positive detections can trigger pool closures, system drain-downs, and costly remediation.

Pseudomonas is strongly associated with biofilm. Pools that struggle with recurring Pseudomonas detections are almost always dealing with a biofilm problem in their pipework or balance tank. Increasing the free chlorine dose treats the symptom (bacteria in the water) but not the cause (bacteria in the biofilm).

ChloroKlean addresses this directly. The sodium hypochlorite component maintains the PWTAG-required free chlorine residual, while the chlorine dioxide generated in situ penetrates and eliminates the biofilm harbouring Pseudomonas colonies.

Disinfection by-products

PWTAG's guidance acknowledges the importance of managing disinfection by-products (DBPs). When free chlorine reacts with organic matter in pool water - sweat, skin oils, urine, cosmetics, and in hydrotherapy pools, animal dander and fur - it produces trihalomethanes (THMs) and haloacetic acids (HAAs). These compounds cause the familiar chlorine smell, eye irritation, and respiratory discomfort that pool users and staff experience.

In hydrotherapy pools and warm-water facilities where organic loading is higher and water temperatures accelerate chemical reactions, DBP formation can be particularly problematic. Staff who spend extended periods in the water face occupational health risks from sustained exposure.

Chlorine dioxide operates through oxidation rather than the substitution reaction that produces THMs and HAAs. The chlorine dioxide generated in situ by ChloroKlean does not produce these harmful by-products, which means:

• No chemical smell above the water surface
• No eye or skin irritation from DBPs
• Reduced respiratory risks for staff in prolonged water contact
• Better air quality in enclosed pool halls

pH sensitivity

PWTAG guidance emphasises the importance of pH control in pool water management. Free chlorine is highly pH-dependent - its disinfecting power drops significantly above pH 7.6. This means pool operators must constantly monitor and adjust pH to keep chlorine effective, adding to the complexity and cost of water management.

Chlorine dioxide is effective across a much broader pH range (pH 4-10), maintaining consistent disinfecting power regardless of pH fluctuations. While the sodium hypochlorite component of ChloroKlean still benefits from proper pH control, the chlorine dioxide provides a safety net of consistent pathogen control even when pH drifts - a common occurrence in busy pools between testing intervals.

PWTAG's Swimming Pool Water book: hydrotherapy pools

The third edition of PWTAG's Swimming Pool Water (2017) specifically covers hydrotherapy pools. This is significant because hydrotherapy pools present unique water treatment challenges compared to standard swimming pools:

• Higher water temperatures (typically 28-34 degrees Celsius) accelerate chemical degradation and bacterial growth
• Higher organic loading from therapeutic activities, and in canine hydrotherapy, from animal fur, dander, and oils
• Prolonged staff immersion - hydrotherapists are in the water for hours, not minutes
• Vulnerable users - patients may have compromised immune systems or open wounds

These are exactly the conditions where ChloroKlean's dual-action chemistry provides the greatest advantage. The sodium hypochlorite base delivers the PWTAG-compliant primary disinfection, while the in-situ chlorine dioxide addresses the elevated biofilm risk, higher organic loading, and the need for effective disinfection at elevated temperatures.

Secondary disinfection: UV and ozone

PWTAG recommends secondary disinfection - typically UV or ozone - as an additional layer of protection, particularly against Cryptosporidium which is resistant to chlorine. ChloroKlean is fully compatible with UV and ozone secondary disinfection systems. The chlorine dioxide generated in situ does not interfere with UV efficacy or ozone treatment, and operates as a complementary layer within the overall water treatment programme.

Water testing and documentation

PWTAG requires regular water testing and comprehensive record-keeping. Pool operators must test and record free chlorine levels, pH, temperature, and other parameters multiple times daily, with monthly UKAS-accredited bacteriological testing.

ChloroKlean supports this requirement by providing:

• A measurable free chlorine residual from the sodium hypochlorite component - tested using standard DPD methods
• Chlorine dioxide residual that can be measured separately using appropriate test methods
• Full product documentation including safety data sheets and technical data sheets
• BPR-compliant product status, providing the regulatory compliance trail that PWTAG expects operators to maintain

The practical position

For pool operators, hydrotherapy centres, and leisure facilities operating under PWTAG guidance, ChloroKlean's position is clear:

ChloroKlean does not replace PWTAG-approved chemistry. It starts with it - sodium hypochlorite, the most widely used approved primary disinfectant - and enhances it with in-situ chlorine dioxide generation for superior biofilm control, broader pathogen efficacy, and a better working environment for pool staff.

"PWTAG sets the standard, and rightly so. ChloroKlean gives operators the confidence that they are meeting that standard with approved chemistry, while solving the biofilm and water quality challenges that chlorine alone struggles to address." - Gavin Owen, Managing Director, ChloroKlean

For a free consultation on how ChloroKlean fits your pool or hydrotherapy water treatment programme, contact our team.