Commercial Pool Water Treatment: Chemical Guide, Dosages & Troubleshooting

Throughout years of supplying swimming pool water treatment chemicals and providing on-site technical support at numerous resorts, hotels, and large residential complexes, the Tan Hung Phu team has observed a recurring reality: pool water issues rarely happen due to a lack of chemicals. Most cases where water suddenly turns algae-green after heavy rain, becomes cloudy, or causes swimmer complaints about strong chlorine odors and eye irritation stem from dosing chemicals by guesswork before baseline parameters are properly balanced.

A standard swimming pool water treatment protocol requires synchronized coordination across functional groups: disinfection & chlorine stabilization (TCCA 90%, Stabilised Chlorine (SDIC 60%), Chlorine 70%, Purex Pool Stabiliser), pH balancing & alkalinity locking (Buffer, pH Increaser Powder Soda Ash Light, HCl balancing solution), algae control & phosphate management (Pool Algaecide, Phosphate Remover), as well as coagulation, heavy metal removal, and water polishing (PAC 31%, Pool Floc, Water Clarifier). This article compiles field-tested experience to help pool operators confidently select the right products, adjust the Langelier Saturation Index (LSI), and resolve three typical water problems at the most optimal cost.

1. Swimming Pool Water Treatment Chemical Groups & Selection Criteria

Each product group addresses a specific link in the water maintenance cycle. The reference table below categorizes the commercial pool care portfolio distributed by Tan Hung Phu:

Water Disinfection: Combining TCCA 90%, Stabilised Chlorine (SDIC 60%), and Chlorine 70%

Sanitizers typically account for the largest share of a pool's maintenance budget. Field experience shows that each chlorine formulation has distinct strengths and should be combined flexibly based on water conditions:

• TCCA 90% (Trichloroisocyanuric Acid): Highly convenient thanks to slow-dissolving 200g tablets that last 5–7 days, ideal for maintaining steady baseline chlorine via an inline feeder or skimmer basket. TCCA contains built-in CYA stabilizer to protect chlorine from intense sunlight. Alongside 200g tablets, Tan Hung Phu supplies quick-sinking Granular TCCA (minimizing dust) and 20g mini-tablets for smaller water volumes.
  Note when placing tablets in the Skimmer: only keep tablets in the basket while the pump is running, and remove them when the pump is turned off. Leaving tablets in stagnant skimmer water creates a localized high-concentration zone that can shorten the lifespan of pumps, filters, and fittings over time. Using a dedicated Feeder/Chlorinator is the most optimal approach.
• Stabilised Chlorine – SDIC 60% (Sodium Dichloroisocyanurate): A stabilized organic chlorine in granule/powder form that dissolves 100% instantly without leaving calcium cloudiness (making it exceptionally compatible with saltwater pools). The greatest advantage of Stabilised Chlorine (SDIC 60%) is its near-neutral pH (~6.0–6.5), allowing effortless daily chlorine top-ups or post-peak-hour boosts with minimal impact on pool pH and Total Alkalinity.
• Calcium Hypochlorite (Chlorine 70%): Dissolves rapidly, delivers immediate oxidation power, and adds zero CYA. It is the ideal choice for algae shock treatments, breaking down Chloramines in pools that already have sufficient CYA, or treating naturally soft water (low calcium hardness).

Balanced Combination Strategy: Use TCCA 90% tablets (or Stabilised Chlorine SDIC 60%) for steady daily baseline sanitation, combined with periodic shock dosing using Chlorine 70%. This approach allows the acidic and alkaline properties of the products to naturally offset each other while keeping CYA safely below 50 ppm over long operating periods.

Technical Safety Note: Never mix organic stabilized chlorines (TCCA, SDIC 60%) directly with inorganic Chlorine 70% in the same bucket or automatic feeder. These products must be dissolved and dosed separately to prevent localized heat reactions and equipment damage.

The Role of Alkalinity Buffering and Phosphate Control

Many technicians encounter constant pH fluctuations: adding pH reducer causes pH to drop too low, while adding pH increaser powder (Soda Ash Light) causes pH to spike. The root cause actually lies in Total Alkalinity (TA). Buffer (Sodium Bicarbonate) re-establishes the bicarbonate buffering system, locking Total Alkalinity at 80–120 ppm to anchor pH steadily within the optimal 7.2–7.6 range.

For outdoor pools surrounded by heavy foliage that experience recurring algae blooms despite proper chlorination, the underlying cause is often accumulated phosphates in the water. In such cases, alongside using Pool Algaecide to eliminate algae cells, operators can consider supplementing with Phosphate Remover to precipitate these nutrients—extending water clarity and reducing long-term maintenance effort.

2. Key Water Quality Parameters to Monitor Closely

Regarding legal regulations in Vietnam, the former Circular 02/2011/TT-BVHTTDL has been replaced by Circular 03/2018/TT-BVHTTDL and Decree 36/2019/ND-CP. Commercial pool operators must ensure feedwater complies with domestic water standard QCVN 01-1:2024/BYT and continuously maintain the following technical reference thresholds:

Water Balance Parameters to Maintain Simultaneously

3. Chemical Principles: pH vs. Active Chlorine, "Chlorine Lock", and LSI Calculation

How pH Affects Chlorine Disinfection Potency

When chlorine dissolves in water, it dissociates into two equilibrium forms: Hypochlorous Acid (HOCl) and Hypochlorite Ion (OCl⁻). Electrically neutral HOCl molecules penetrate cell walls and destroy bacteria and algae 80–100 times faster than OCl⁻ ions.

• At pH = 7.2: Approximately 66% of free chlorine exists as powerful sanitizing HOCl.
• At pH = 7.5: The HOCl ratio is roughly 49% – the optimal sweet spot balancing strong disinfection with swimmer eye and skin comfort.
• When pH rises to 8.0: Active HOCl drops sharply to only ~21%. At this point, even if test kits show sufficient chlorine residual, nearly 80% of the chlorine is sluggish, allowing green algae to bloom easily.

"Chlorine Lock" Caused by CYA Accumulation

Cyanuric Acid binds to chlorine to shield it from UV photolysis. However, CYA does not evaporate. When TCCA or SDIC is used continuously with minimal backwash water replacement, CYA levels can exceed 100 ppm, significantly lowering the water's Oxidation-Reduction Potential (ORP). Chlorine becomes "locked" and cannot release quickly enough to sanitize. To resolve this, operators must partially drain and dilute the pool with fresh water and switch to Chlorine 70% for shock dosing.

Relationship Between Free Chlorine and CYA

Because CYA holds onto a portion of chlorine in reserve, higher CYA levels require maintaining a higher Free Chlorine baseline. Many professional operators apply the following ratio:

Langelier Saturation Index (LSI) Formula

The LSI indicates the calcium carbonate saturation balance of water, helping prevent material wear or scaling before damage occurs:

Where: TF is Temperature Factor; CF is Calcium Hardness Factor; AF is Corrected Alkalinity Factor (Corrected Alkalinity = TA − [CYA ÷ 3]); and TDSF is the Total Dissolved Solids constant (12.1 for standard freshwater pools, 12.2 for saltwater chlorinator pools).

LSI Calculation Example at 29 °C: Measured pH = 7.4 · Calcium Hardness = 250 ppm · TA = 110 ppm · CYA = 30 ppm · Freshwater (TDSF = 12.1).
Corrected Alkalinity = 110 − (30 ÷ 3) = 100 ppm. From the table: TF = 0.7; CF = 2.0; AF = 2.0.
LSI = 7.4 + 0.7 + 2.0 + 2.0 − 12.1 = 0.0 – Perfectly balanced water; no adjustment needed.

Result Evaluation: Water is ideally balanced when LSI falls between −0.3 and +0.3. If LSI < −0.3, water tends to etch pool walls, tile grout, and metal fittings. If LSI > +0.3, water is over-saturated and prone to depositing calcium scale, dulling tiles and fouling salt chlorinator cells.

4. Technical Protocols for Resolving Three Common Issues in a 300 m³ Commercial Pool

Below are standardized recovery procedures that restore water quality rapidly at a fraction of the cost of draining and refilling the pool, modeled on a standard 300 m³ commercial pool (reference dimensions: 25 m × 8 m × 1.5 m):

Issue 1: Pool Water Turns Algae-Green After Heavy Rainstorms

1. Brush Surfaces & Balance pH (Step 1): Thoroughly brush tile grout lines to break up protective algae biofilms. Test the water: if Total Alkalinity (TA) dropped to 60 ppm, dose 9 kg of Buffer to bring TA back to 80 ppm, then adjust pH to 7.2.
2. High-Level Chlorine Shock (Step 2 - Perform in late afternoon): Raise Free Chlorine to 10 ppm to eradicate algae cells (if CYA exceeds 30 ppm, scale chlorine dosage according to Section 3). Pre-dissolve and broadcast 4.3 kg of Chlorine 70% evenly around the pool with the circulation pump running continuously.
3. Dose Algaecide & Prevent Recurrence (Step 3): Pour 3–4.5 liters of Pool Algaecide evenly around the pool perimeter to eliminate remaining algae roots. Once the water turns milky-cloudy (indicating dead algae), you can proceed directly to Step 4 to optimize treatment costs. (Advanced Optional Step: For outdoor pools with heavy leaf fall or frequent recurring algae blooms, operators may supplement with Phosphate Remover to strip reserve nutrients—ensuring long-term water stability while remaining far more economical than draining and replacing the entire pool volume).
4. Overnight Static Flocculation (Step 4): Set the multiport valve to Recirculate (bypassing the sand bed), pre-dissolve 1.5–3.0 kg of Pool Floc or PAC 31%. Run the pump for 30 minutes to disperse evenly, then shut off the pump completely for 8–10 hours.
5. Vacuum Sediment to Waste (Step 5): The next morning, switch the multiport valve to Waste and vacuum the pool floor slowly to discharge settled sediment directly to the drain. Top up lost water and dose Water Clarifier to restore a sparkling, crystal-clear finish.

Issue 2: Pungent Chlorine Odor and Eye Irritation

A sharp chemical smell occurs when Combined Chlorine (Chloramines) exceeds 0.2 ppm due to insufficient Free Chlorine to completely oxidize organic nitrogen compounds from swimmer sweat.

Breakpoint Chlorination for a 300 m³ Pool: If Combined Chlorine measures at 0.8 ppm, you must add Free Chlorine equal to 10 times that value—equivalent to 8.0 ppm of active chlorine. The pure chlorine mass required is 2.4 kg (300 m³ × 8 g/m³). Using Chlorine 70% to avoid raising CYA, the actual product weight needed is 3.43 kg. Perform shock treatment at night with continuous filtration to completely destroy Chloramines, restoring odor-free, gentle water.

Issue 3: Water Turns Brownish-Yellow or Dark Green When Using Well Water

Groundwater from boreholes often contains dissolved heavy metal ions such as Iron (Fe²⁺), Manganese (Mn²⁺), and Copper. When oxidizing chlorine is added, these ions precipitate into suspended metal oxides, tinting the water tea-yellow or dark brown and staining tiles.

Intervention for a 300 m³ Pool: First, check and stabilize alkalinity using Buffer and slightly raise pH to 7.5–7.6 (using Soda Ash Light pH increaser powder) to accelerate complete metal precipitation. Next, set the filter valve to Recirculate, pre-dissolve 2.0–3.0 kg of PAC 31% (or Pool Floc), distribute evenly across the pool, circulate for 30 minutes, then shut off the pump to settle overnight (8–12 hours). The next morning, switch the valve to Waste and vacuum the settled metallic sludge from the bottom. Finally, resume normal filtration and dose 500–750 ml of Water Clarifier to trap remaining micro-particles in the sand filter and restore crystal clarity.

Do Not Overlook Mechanical Factors: Circulation & Filtration

Water treatment products only perform at their best when water is properly circulated and filtered. Recurring issues despite accurate chemical dosing often stem from mechanical bottlenecks:

• Turnover Rate: Main commercial pools are typically designed to turn over their entire water volume every 4–6 hours; wading pools and spas require much faster turnover. Running pumps for insufficient hours creates "dead spots" where algae begins to grow.
• Backwashing: Perform a backwash when the filter pressure gauge rises by 0.5 bar (7–8 psi) above the clean starting pressure, or on a fixed schedule. Filter sand that is clumped or channeled after 5–7 years should be replaced.
• Bather Load: Peak swimming hours cause Combined Chlorine to rise rapidly. Test Total and Free Chlorine immediately after high-traffic periods.
• Swimmer Hygiene: Enforcing pre-swim showers significantly reduces sweat, sunscreen, and hair oils—the primary precursors to Chloramines and Phosphates.

5. Standard Dosing Reference Table (per 100 m³ of Water) & Testing Frequency

* Dosages are for reference under standard conditions. Always dose half the estimated amount first, circulate for 1–2 hours, and retest before adding more. Only use Purex Pool Stabiliser for outdoor pools not yet using TCCA/SDIC or when CYA is below 30 ppm.

Routine Water Testing Schedule for Operators

6. Storage & Handling Guidelines for Pool Care Products

Sanitizing and pH-balancing products are formulated in concentrated form to treat large volumes of water efficiently. Once properly dissolved and balanced in the pool, the water is completely safe and gentle for swimmers. During storage and initial preparation, operators should follow these standard technical practices:

• Storage: Keep in a cool, dry, well-ventilated area away from direct sunlight; reseal packaging tightly after each use. Store TCCA, Stabilised Chlorine (SDIC 60%), Chlorine 70%, and pH-adjusting liquids on separate shelves/zones away from oils or flammable materials.
• Independent Handling: Never mix different types of chlorine together, and never mix chlorine with pH-reducing solutions in the same container. Use a dedicated, clean, dry measuring cup for each product.
• Standard Dilution Sequence: Always add chemicals slowly into water when pre-dissolving; never pour water directly onto concentrated products. Dose different product groups at least a few circulation hours apart, or follow label instructions.
• Personal Protective Equipment (PPE): Wear chemical-resistant gloves, safety goggles, and a mask when measuring and mixing; handle in well-ventilated spaces.
• Documentation: Keep Material Safety Data Sheets (MSDS) and Certificates of Analysis (COA) on file for each batch, and train staff on standard operating procedures.

7. Frequently Asked Questions (FAQ) About Pool Water Treatment

8. Scientific Basis & International Reference Standards

The technical protocols and parameters presented in this article are cross-referenced with peer-reviewed research and international recreational water health guidelines:

• Impact of Cyanuric Acid on Chlorine Disinfection Kinetics (NCBI PubMed): Scientific study published in the Journal of Water and Health demonstrating how high CYA accumulation significantly extends the pathogen inactivation time of free chlorine. Reference: NCBI PubMed – Relationship between cyanuric acid and free chlorine on disinfection efficacy.
• Eye Irritation Causes & Indoor Pool Air Quality (U.S. CDC): Guidelines from the U.S. Centers for Disease Control and Prevention identifying Chloramines as the primary cause of eye irritation and respiratory discomfort in swimming pools. Details at: CDC Healthy Swimming – Chemical Irritants & Indoor Pool Air Quality and CDC Model Aquatic Health Code (MAHC).
• Safe Recreational Water Environments (World Health Organization - WHO): Standardized WHO guidelines on turbidity control, sand filtration coagulation, and microbial indicator limits in public pools: WHO Guidelines for Safe Recreational Water Environments – Volume 2.
• CPO® Water Quality & Operational Standards (PHTA USA): ANSI/APSP/ICC technical standards on water chemistry balance and LSI calculation from the Pool & Hot Tub Alliance: PHTA Standards & Codes.
• Legal Framework in Vietnam: Regulations on facilities and technical standards for swimming and diving activities under Circular 03/2018/TT-BVHTTDL.