How Much 1-3 mm Sodium Thiosulfate Pentahydrate Should You Dose to Neutralize Chlorine in Water
2026-10-16
Determining the correct dosage of 1-3 mm Sodium Thiosulfate Pentahydrate is essential for anyone tasked with removing chlorine from water, whether in an aquarium, a municipal pool, or an industrial wastewater stream. V&S has supplied this crystalline compound to water treatment professionals for years, and the most common question we receive is deceptively simple: how much do you actually need? The answer depends on chlorine concentration, water volume, and the form of chlorine present, but the chemistry itself is predictable and easy to apply once you understand the stoichiometry.
The Chemistry Behind the Dose
Chlorine neutralization with 1-3 mm Sodium Thiosulfate Pentahydrate follows a well-established redox reaction. Thiosulfate reduces free chlorine and chloramine to chloride, which is harmless at typical concentrations. The practical rule most operators memorize is that roughly 2.6 mg of sodium thiosulfate pentahydrate neutralizes 1 mg of free chlorine. However, because V&S supplies a granular 1-3 mm Sodium Thiosulfate Pentahydrate rather than a fine powder, dissolution rate and bulk density slightly affect how quickly the reaction completes in cold or poorly mixed water.
Quick Reference Dosing Table
| Chlorine Level (mg/L) | Water Volume (L) | 1-3 mm Sodium Thiosulfate Pentahydrate Required |
|---|---|---|
| 1 | 100 | 0.26 g |
| 2 | 100 | 0.52 g |
| 5 | 100 | 1.30 g |
| 1 | 1,000 | 2.60 g |
| 2 | 1,000 | 5.20 g |
| 5 | 1,000 | 13.0 g |
For chloramine, multiply the result by approximately 1.5, since breaking the nitrogen-chlorine bond consumes additional thiosulfate.
Step-by-Step Dosing Procedure
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Measure free and total chlorine using a DPD kit or colorimeter before treatment.
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Calculate the mass of 1-3 mm Sodium Thiosulfate Pentahydrate using the 2.6:1 ratio, then adjust for chloramine if present.
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Dissolve the granules in a small volume of warm water to accelerate dissolution of the 1-3 mm Sodium Thiosulfate Pentahydrate.
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Add slowly to the bulk water with agitation, never the reverse.
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Retest after 15 minutes and top up in small increments if residual chlorine remains.
V&S recommends preparing a 10% stock solution for large facilities, which improves accuracy and reduces dust exposure compared with weighing dry granules for every batch.
Factors That Shift the Required Dose
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pH above 8.0 slows the reaction and may require a 10–20% overdose.
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Temperature below 10°C extends contact time; pre-dissolving the 1-3 mm Sodium Thiosulfate Pentahydrate becomes critical.
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High organic load consumes chlorine independently, so always base the calculation on measured residual, not the original dose applied.
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Excess thiosulfate can depress dissolved oxygen, so avoid gross overdosing in aquaculture systems.
1-3 mm Sodium Thiosulfate Pentahydrate FAQ
Q: How fast does 1-3 mm Sodium Thiosulfate Pentahydrate neutralize chlorine in a large tank?
A: When pre-dissolved and added with moderate agitation, neutralization is typically complete within 2 to 5 minutes at room temperature. In cold water below 10°C, allow 10 to 15 minutes and verify with a DPD test before discharging or introducing aquatic life.
Q: Can I use 1-3 mm Sodium Thiosulfate Pentahydrate to remove chloramine as well as free chlorine?
A: Yes, but chloramine requires a higher dose because the ammonia fraction must also be addressed. Multiply the free-chlorine calculation by about 1.5, and monitor ammonia separately if the water is destined for sensitive biological systems.
Q: Is overdosing 1-3 mm Sodium Thiosulfate Pentahydrate dangerous for fish or downstream processes?
A: Mild excess is generally tolerated, but a large overdose can consume dissolved oxygen and interfere with certain analytical tests. Dose to the measured chlorine residual, retest, and add only incremental top-ups rather than a single large excess.
Q: What purity should I look for when buying 1-3 mm Sodium Thiosulfate Pentahydrate?
A: For potable water and aquaculture, select a minimum 99% assay with low heavy-metal content. V&S supplies technical and high-purity grades with batch-specific certificates of analysis, which simplifies regulatory documentation.
Contact Us
Ready to standardize your chlorine neutralization program with a reliable supplier? Contact V&S today for a customized quotation, a free dosing consultation, and a sample of our 1-3 mm Sodium Thiosulfate Pentahydrate. Our technical team will help you calculate the exact dose for your water volume and chlorine profile, ensuring compliance and cost efficiency from the first batch.