How to Use TCCA (Trichloroisocyanuric Acid) for Water Disinfection

Overview

Trichloroisocyanuric Acid (TCCA, CAS 87-90-1) is the most concentrated solid chlorine disinfectant available, with ≥ 90% available chlorine content — significantly higher than SDIC (sodium dichloroisocyanurate, 56% available chlorine) and sodium hypochlorite solution (10–15%). Its slow-dissolving tablet and granular forms make it ideal for sustained chlorination in automatic chemical feeders and floating dispensers, rather than the instantaneous release of granular forms.

TCCA dissolves to release hypochlorous acid (HOCl), the active germicidal species, and cyanuric acid (CYA), which acts as a UV stabilizer for outdoor pools. One gram of TCCA dissolving in water releases approximately 0.9 g of available chlorine while producing 0.6 g of cyanuric acid.

Key use cases: continuous swimming pool disinfection (tablets in floating dispensers or skimmer feeders), cooling tower shock chlorination, and emergency/field drinking water disinfection. TCCA is NOT approved for use in municipal drinking water treatment in most countries — for that application, use sodium hypochlorite or chlorine gas.

Preparation & Dissolution

For tablet feeders (swimming pools and cooling towers):

1. Load tablets into automatic feeder: Place 200 g tablets into the in-line automatic chlorinator or floating dispenser. Do not crush or break tablets — allow them to dissolve slowly as water flows over them.
2. Set flow rate: Adjust the feeder bypass valve to control water contact time with the tablets. Higher flow = faster dissolution = more chlorine release. Most feeders have a dial marked 1–10 corresponding to % bypass.
3. Check available chlorine: After 1–4 hours of recirculation, test free chlorine at the return fitting. Adjust feeder setting to achieve target residual.
4. Never mix TCCA tablets with other chemicals: TCCA tablets must be loaded dry. Never mix TCCA with any other pool chemical (including other chlorine products, pH adjusters, or algaecides) in the feeder — violent reactions, fire, or explosion can result.

For shock treatment (granules dissolved in water):

1. Pre-dissolve in a plastic bucket: Add TCCA granules to a full bucket of clean water (never add water to TCCA granules). Use 1 kg granules per 10 L water to make a 10% slurry. Wear chemical-resistant gloves and eye protection.
2. Stir until dissolved: TCCA granules dissolve more slowly than SDIC — allow 10–15 minutes with stirring.
3. Add to pool/system with circulation running: Pour the dissolved slurry slowly around the perimeter or directly into the skimmer, never directly into the return jets or onto pool surfaces.

Dosing Guide

Application	TCCA Dose	Free Chlorine Target	Notes
Swimming pool — daily maintenance	2–5 g per m³ water/day	1.0–3.0 mg/L	Via tablet feeder; depends on bather load
Swimming pool — shock treatment	10–20 g per m³	Temporarily 5–10 mg/L	Wait for residual to drop < 3 mg/L before swimming
Cooling tower — continuous	1–3 mg/L free chlorine maintained	0.5–2.0 mg/L	Lower dose if other biocides used in rotation
Cooling tower — shock chlorination	5–10 mg/L free Cl₂, 4–6 hour contact	> 5 mg/L during shock	Monthly or after Legionella concern
Emergency drinking water disinfection	1 tablet (3.3 g, 200 mg Cl) per 100 L	0.2–0.5 mg/L after 30 min	Field emergency only; not for routine DW use
Fish pond (disease treatment)	0.3–0.5 mg/L	Maintain for 24 hours	Sensitive to fish species; test first

Application Procedure

Swimming pool (continuous):

1. Maintain pool water pH at 7.2–7.6 before adding TCCA. At pH > 7.8, HOCl is largely converted to OCl⁻ (10x less germicidal). At pH < 7.0, equipment corrosion and eye irritation increase.
2. Load tablets into automatic chlorinator or floating dispenser. One standard 200 g TCCA tablet provides approximately 180 g available chlorine.
3. For outdoor pools: cyanuric acid from TCCA builds up over time. Check CYA level monthly. Target 30–50 mg/L CYA. Above 80 mg/L, chlorine effectiveness is significantly reduced ("chlorine lock") — dilute by backwashing or partial water exchange.
4. Test free chlorine at least twice daily (morning and after peak bather load). Adjust feeder setting to maintain 1.0–3.0 mg/L.

Cooling tower shock chlorination:

1. Reduce tower blowdown rate and allow cycles of concentration to stabilize first.
2. Dissolve calculated TCCA dose in a plastic bucket (10% solution), add slowly to tower basin with circulation pump running.
3. Circulate at 5–10 mg/L free chlorine for 4–6 hours. Check free chlorine at 30-minute intervals — if it drops below 2 mg/L in less than 2 hours, the system has high biofilm load and may require another shock dose.
4. After shock treatment, resume normal biocide rotation and blowdown.
5. Conduct Legionella risk assessment and add TCCA shock to the risk management plan with documented records.

Monitoring & Control

Parameter	Frequency	Target
Free chlorine (swimming pool)	Twice daily (minimum)	1.0–3.0 mg/L
Combined chlorine (chloramines)	Daily	< 0.5 mg/L (odor threshold)
pH	Twice daily	7.2–7.6
Cyanuric acid (outdoor pool)	Monthly	30–50 mg/L; action at > 80 mg/L
Turbidity (pool water)	Daily	< 0.5 NTU
Free chlorine (cooling tower)	Daily	0.5–2.0 mg/L (residual)
Legionella testing (cooling tower)	Quarterly	< 100 CFU/L; < 1 CFU/L after shock
Total dissolved solids (pool)	Monthly	< 1500 mg/L; dilute if higher

Common Mistakes

• Mixing TCCA with other pool chemicals: TCCA mixed with calcium hypochlorite (HTH/bleaching powder), SDIC, or pool algaecides (especially those containing ammonium compounds) causes immediate violent reactions including fire and chlorine gas release. Never store TCCA in the same cabinet as other pool chemicals. Never mix dry TCCA with anything — always dissolve in clean water first.

• Adding TCCA directly onto pool surfaces: Concentrated TCCA solution (pH 2.5–3.5) bleaches and etches pool liners, plaster, and vinyl surfaces. Always pre-dissolve in a bucket and distribute around the perimeter with circulation running, or add through the skimmer.

• Allowing cyanuric acid (CYA) to accumulate above 80 mg/L: In outdoor pools where TCCA is the only chlorine source, CYA builds up irreversibly. Above 80 mg/L, CYA forms a complex with HOCl that drastically reduces germicidal activity — pools can have measurable free chlorine but still test positive for E. coli. Partial drain and refill is the only remedy. Use CYA-free sodium hypochlorite periodically to manage CYA accumulation.

• Not adjusting dose for bather load and weather: On busy summer days with 5x normal bather load, the chlorine demand can triple. Many pool operators set a fixed tablet feeder position and never adjust. A single heavy-use weekend can deplete chlorine to < 0.5 mg/L, creating a sanitization failure. Monitor free chlorine before and after peak periods.

• Using TCCA for routine municipal drinking water treatment: TCCA introduces cyanuric acid into treated water. CYA has no taste-and-odor threshold that allows consumers to detect it, and there is no WHO/EPA guideline value established for CYA in drinking water. TCCA is approved only for emergency/field use in drinking water, not as a substitute for sodium hypochlorite or chlorine gas in municipal treatment.

Storage & Handling

• Store in a cool, dry, well-ventilated area away from heat sources, open flames, and incompatible chemicals (oxidizers, acids, reducing agents, nitrogen-containing compounds).
• TCCA is a strong oxidizer — store separately from any organic materials, oils, and fuels.
• Containers must remain sealed when not in use. Moisture causes TCCA to degrade and release chlorine gas.
• Wear chemical-resistant gloves, eye protection, and acid/chlorine-resistant clothing when handling. TCCA dust and vapors are respiratory irritants — work in ventilated areas.
• In case of fire involving TCCA, use large amounts of water — do not use CO₂ or dry powder extinguishers.
• Shelf life: 3 years in sealed drums in dry conditions below 30°C.