Sodium Hypochlorite 12.5% (Liquid Chlorine): An Industrial Dosing and Buying Guide
Sodium hypochlorite, sold as liquid chlorine, is the workhorse disinfectant and oxidiser for many Australian businesses. Cooling towers, wastewater plants, food factories, water carriers and cleaning contractors all use it. It is easy to dose, effective and economical, but only if you buy the right strength, calculate doses correctly, and store it so it does not lose strength or create a hazard. This guide is written for plant and maintenance managers, facility operators and procurement teams.
What does “12.5%” actually mean?
Sodium hypochlorite strength is usually expressed as available chlorine. Viva Blu’s sodium hypochlorite 12.5% is 12.5% w/v available chlorine, which is 125 grams of available chlorine per litre. Many retail and pool products are 10% (100 g/L). Comparing on grams of chlorine per litre, rather than price per container, is the fairest way to compare suppliers: 12.5% delivers 25% more chlorine per litre than 10%.
The dosing formula
Because 1 mg/L equals 1 g per 1,000 L, the maths is simple:
Volume of 12.5% hypochlorite (mL) = target dose (mg/L) x water volume (kL) x 8
That works because 1 g of chlorine is contained in 8 mL of a 125 g/L solution. Examples:
- Raise 10 kL by 2 mg/L: 2 x 10 x 8 = 160 mL
- Disinfect a 5 kL tank at 50 mg/L: 50 x 5 x 8 = 2,000 mL (2 L)
- Shock a 30 kL cooling system to 5 mg/L: 5 x 30 x 8 = 1,200 mL
These figures are the chlorine you add. The residual you measure will be lower if the water has chlorine demand (organics, ammonia, iron, biofilm). Always dose, mix, wait and test.
Indicative targets by application
| Application | Typical target | Practical notes |
|---|---|---|
| Cooling tower, routine control | 0.5 to 2.0 mg/L free chlorine | Continuous or timed dosing by metering pump, as set out in the site water management or risk management plan |
| Cooling tower, shock or restart | 5 to 10 mg/L free chlorine, at least 1 hour contact | Adjust pH to about 7.0 to 7.6 first; manage blowdown discharge |
| Water tank or line disinfection | 50 mg/L, 30 minutes contact | About 400 mL per kL; flush before return to service; follow water authority requirements |
| Wastewater, terminal disinfection | 5 to 20 mg/L, 30 minutes contact | Needs low turbidity to work; dechlorinate before discharge if your licence requires |
| Food plant hard surfaces | 1:50 to 1:100 dilution | 5 to 10 minutes contact, then rinse per food safety program |
| Exterior pressure cleaning | 1:10 to 1:20 dilution | Protect plants and stormwater; rinse thoroughly |
These are indicative ranges. Confirm against your site plan, your water treatment provider’s program and on-site testing. pH matters: chlorine is a much stronger disinfectant at pH 7.0 to 7.6 than at pH 8 and above.
Cooling towers: know your state rules
Hypochlorite is a common oxidising biocide in cooling water. Cooling water systems in Australia are managed under the AS/NZS 3666 series (microbial control of air-handling and water systems of buildings) and state-based public health rules, which differ:
- Queensland: the WorkSafe Queensland Guide to Legionella control in cooling water systems, including cooling towers refers to AS/NZS 3666 parts 1 to 4 for design, operation and maintenance.
- New South Wales: NSW Health states that the Public Health Regulation 2022 requires cooling water systems to be managed according to AS/NZS 3666.3:2011, with monthly Legionella and heterotrophic colony count testing, a risk management plan and annual independent audits.
- Western Australia: WA Health summarises legislation and guidelines for cooling towers and water systems.
Chemical choice and dose should sit inside that framework, ideally with a water treatment specialist. Viva Blu supplies the chemical; it does not replace your risk management plan.
Strength loss: why fresh stock matters
Sodium hypochlorite slowly decomposes in storage. It loses strength faster when warm, in sunlight, or when contaminated with metals. In practice this means:
- Buy volumes you will use promptly, because sodium hypochlorite loses strength over time.
- Store containers cool and dark and out of hot plant rooms where possible.
- Use stock in rotation (first-in, first-out), and do not top up old stock with new.
- If doses suddenly seem to “stop working”, test the stock strength before increasing dose rates.
Dosing equipment tips
- Use metering pumps with chemically compatible wetted parts, for example PVDF or suitable PVC heads with FKM (Viton) seals. Viva Blu stocks dosing pumps with PVDF heads and PVC heads.
- Hypochlorite can gas off in suction lines and pump heads, causing vapour lock. Keep suction lines short, use flooded suction where possible and choose pumps with degassing features if gassing is a problem.
- Avoid metals in contact with concentrated hypochlorite: mild and galvanised steel, copper, brass and aluminium are attacked.
- Pair dosing with monitoring, for example a pH probe and controller.
Storage, segregation and safety
Sodium hypochlorite 12.5% is a dangerous good: UN 1791, Class 8 (Corrosive) with a 5.1 (Oxidising) subsidiary risk. Read the Safety Data Sheet and add it to your hazardous chemicals register.
- Keep away from acids. Hypochlorite and acids (hydrochloric, sulphuric, citric, even “pH down” products) release toxic chlorine gas. This is one of the most common serious chemical incidents on water treatment sites. Use separate bunds, separate dosing points and clearly labelled lines.
- Bund it. WHS regulation 357 (for example in Queensland) requires spill containment where there is a spill risk, and Safe Work Australia’s storage guide says incompatible chemicals should never share bunding. See our guide to chemical bunding requirements in Australia and our chemical spill bunds.
- Also keep apart from ammonia compounds, hydrogen peroxide, calcium hypochlorite and organics.
- PPE: nitrile or neoprene gloves, goggles or a face shield, and protective clothing. Use respiratory protection where vapours may build up.
- First aid: flush skin or eyes with water for at least 15 minutes. Poisons Information Centre: 13 11 26.
Buying checklist for procurement
- Strength: compare g/L of available chlorine, not just price per container.
- Freshness: ask about manufacture date and plan volumes to suit your usage rate.
- Documents: a current SDS.
- Pack size: match container size to your handling equipment and usage. Viva Blu supplies 5 L and 20 L.
- Freight: hypochlorite ships as a dangerous good, so confirm delivery lead times to your site.
- Account: set up trade buying for repeat orders.
Also used in pools
The same 12.5% product is used by commercial and residential pool operators: about 80 mL raises free chlorine by 1 ppm per 10,000 L. See how much chlorine to shock a pool.
Buy sodium hypochlorite 12.5% from Viva Blu
Viva Blu supplies sodium hypochlorite 12.5% (liquid chlorine) in 5 L and 20 L containers from our Brisbane warehouse in Windsor, QLD. Delivery is Australia-wide with dangerous goods freight calculated at checkout, and free pickup is available. Businesses can register for a B2B account, or call 0402 981 808 or email contact@vivablu.com.au to discuss regular supply.
Frequently asked questions
What does 12.5% sodium hypochlorite mean?
It means 12.5% w/v available chlorine, which is 125 grams of available chlorine per litre. A 10% product contains 100 g/L, so 12.5% gives 25% more chlorine per litre.
How do I calculate a sodium hypochlorite dose?
For a 12.5% product, millilitres needed = target dose in mg/L x water volume in kilolitres x 8. For example, 2 mg/L in 10 kL needs about 160 mL, before any chlorine demand.
What free chlorine level is used in cooling towers?
Routine control commonly maintains about 0.5 to 2.0 mg/L free chlorine, with higher shock doses for remediation. Targets should follow your site risk management plan, AS/NZS 3666 and your state health requirements.
How long does sodium hypochlorite last?
It slowly loses strength, faster in heat and sunlight. Store it sealed, cool and dark, use stock in rotation, and buy volumes you will use promptly.
Can sodium hypochlorite be stored with acids?
No. Mixing hypochlorite with acids releases toxic chlorine gas. Store and bund them separately and use separate dosing lines.
What pack sizes does Viva Blu supply?
Sodium hypochlorite 12.5% is available in 5 L and 20 L containers. For regular supply, register for a B2B account or call 0402 981 808.