Use this for a fixed volume of chlorinated water in a tank, reservoir or basin. Two common jobs:
Enter the tank volume, the measured chlorine residual and your target. Pick an agent and how you will dose it. The tool returns the quantity to add, the environmental impact of any excess, and mixing and verification guidance.
The tool does the maths — you enter what you can measure on site.
Enter what you know. With starting pH and alkalinity the tool predicts the pH after dosing. Temperature refines the estimate and the contact-time guidance.
Use this for chlorinated water in a pipeline. Two common jobs:
Batch mode treats the standing volume in the line. Continuous injection mode gives a dosing rate for feeding agent into a flush stream at the discharge point.
Chlorine is acutely toxic to aquatic life at very low concentrations, so superchlorinated flush water must never reach a waterway untreated.
Enter what you know. With starting pH and alkalinity the tool predicts the pH after dosing. Temperature refines the estimate and the contact-time guidance.
An operations aid for neutralising chlorine in tanks and pipelines before discharge or return to service.
All doses derive from the balanced reaction of each agent with chlorine, expressed on a Cl₂ basis. The mg/mg column is milligrams of pure agent per milligram of Cl₂ removed; these are editable in Settings. The alk column is alkalinity destroyed (mg/L as CaCO₃) per mg/L of Cl₂ removed.
| Agent | mg/mg | alk | DO? |
|---|
Thiosulphate is modelled on the complete-oxidation (sulphate) pathway, which dominates when chlorine is in excess — the usual dechlorination condition. At very low chlorine it partly oxidises only to tetrathionate and consumes far more agent, so a safety excess and a confirmatory test are advised.
The sulphur-based agents (SO₂, sulphite, bisulphite, metabisulphite, thiosulphate) are oxygen scavengers. Any excess that reaches the receiving water strips dissolved oxygen: about 0.23 mg/L of DO for every 1 mg/L (as Cl₂) of excess reducing capacity. On sensitive receiving waters this favours a tight safety excess, or an ascorbate, which does not consume oxygen.
Every one of these reactions produces strong acid (HCl, and bisulphate or sulphuric acid), which consumes alkalinity and lowers pH. The acid load is fixed by the chlorine removed, not by the dose, so a safety excess does not add to it. If you enter starting pH and alkalinity the tool predicts the pH after dosing from the carbonate system, and warns when alkalinity is largely consumed and pH is at risk of crashing. Sodium ascorbate is the gentlest on pH; SO₂, bisulphite and metabisulphite are the harshest.
Temperature has a secondary but real effect. Colder water slows the reactions — a minor issue for free chlorine, which reacts in seconds, but combined chlorine in cold water needs more contact time. Temperature also shifts the carbonate equilibrium constants used in the pH prediction, and colder water holds more dissolved oxygen, so a given oxygen draw from excess reductant is a smaller share of the baseline.
Free chlorine reacts with these agents in seconds once mixed — the limiting step is achieving complete mixing. Combined chlorine (chloramine) reacts more slowly; allow several minutes of contact before verifying.
Always re-test the residual after treatment and mixing, and confirm it meets your discharge consent or service target before releasing or returning to service.
Guidance tool only. Confirm doses against site procedures, product data sheets and your discharge consent. Chlorine receiving-water guideline triggers are very low (order 0.003 mg/L) — check the limit that applies to you.
mg of pure agent per mg of Cl₂ removed. Defaults are the stoichiometric values; adjust for a site-specific or product-specific figure.