📖 How To Use
How to Use This Potassium Permanganate Dosage Calculator
Getting the correct KMnO₄ dose for your water tank takes under a minute:
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Enter your tank volume
Input the total volume of water to be treated. Use the unit selector to switch between litres, cubic metres, US gallons, or UK gallons. For partially filled tanks, enter only the volume of water currently in the tank, not total capacity.
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Set your target dose
Select the concentration you need in mg/L (milligrams per litre) or ppm — these are equivalent for water. Typical dosing ranges: 2–5 mg/L for oxidation of iron and manganese, 5–10 mg/L for algae control, 10–20 mg/L for shock disinfection of storage tanks.
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Enter KMnO₄ purity (optional)
Standard technical-grade potassium permanganate is 97–99% pure. If your product label states a specific purity, enter it here so the calculator adjusts the dose accordingly. Leave at 99% if unsure.
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Read your results
The primary result shows the exact grams of KMnO₄ to dissolve and add to your tank. Secondary outputs include the concentration category, recommended contact time, and a reminder to neutralise or flush after treatment.
Safety note: Always dissolve KMnO₄ crystals in a small volume of water before adding to the tank — never add crystals directly to a full tank. Wear gloves and eye protection. Potassium permanganate stains skin and surfaces dark brown/black on contact.
📐 The Formula
Potassium Permanganate Dosage Formula
The mass of KMnO₄ required is simply the volume of water multiplied by the target concentration:
KMnO₄ (grams) = Volume (litres) × Dose (mg/L) ÷ 1,000
Purity-adjusted: KMnO₄ (g) = [V (L) × D (mg/L) ÷ 1,000] ÷ (Purity% ÷ 100)
Example: 5,000 L tank at 4 mg/L = 5,000 × 4 ÷ 1,000 = 20 grams
Since 1 mg/L is numerically identical to 1 ppm (parts per million) for dilute aqueous solutions, the formula applies equally whether you use mg/L or ppm as your concentration unit.
Standard Dosage Reference Guide
| Application | Typical Dose | Contact Time | Notes |
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| Iron oxidation | 1–3 mg/L | 15–30 min | Followed by filtration |
| Manganese oxidation | 2–5 mg/L | 30–60 min | pH > 7.5 increases efficiency |
| Algae & taste/odour control | 5–10 mg/L | 30 min+ | Flush or filter after treatment |
| Tank disinfection (shock) | 10–20 mg/L | 60–120 min | Drain and refill after treatment |
| Zebra mussel control | 2–4 mg/L | 4–12 hours | Industrial/agricultural use only |
| Hydrogen sulphide removal | 3–8 mg/L | 30–60 min | Check for pink residual colour |
How to Check Dosage is Correct
After dosing, the water should turn a pink to violet colour. A faint pink tinge indicates the permanganate has been consumed (treating iron, manganese, or organic matter). A persistent deep violet or purple colour means excess KMnO₄ remains and the water must not be consumed until the colour clears — either through natural decay or by adding a reducing agent such as sodium thiosulphate to neutralise it.
💡 Use Cases
When to Use Potassium Permanganate for Water Treatment
1. Iron & Manganese Removal from Bore Water
KMnO₄ is one of the most effective oxidants for converting dissolved iron and manganese into insoluble particles that can then be filtered out. This is common for bore holes and well water where metallic taste and rust-coloured staining are problems. A dose of 1–3 mg/L followed by sand filtration is the standard approach.
2. Seasonal Tank Disinfection
Water storage tanks accumulate biofilm and bacterial growth over time, especially in warm climates. A shock dose of 10–20 mg/L, left to stand for 1–2 hours with the tank emptied and refilled, effectively disinfects surfaces and the stored water. This is particularly important before the monsoon season or after extended periods of stagnation.
3. Algae Control in Rooftop & Open Tanks
Open or inadequately sealed tanks develop algal blooms that cause taste, odour, and turbidity problems. A dose of 5–10 mg/L suppresses algal growth. Treat in the evening to avoid UV degradation of the permanganate before it can act.
4. Hydrogen Sulphide (Rotten Egg Smell) Treatment
Groundwater with sulphate-reducing bacteria produces H₂S, which KMnO₄ oxidises efficiently. Doses of 3–8 mg/L typically eliminate the odour within an hour.
Important: Potassium permanganate is not a substitute for regular chlorination or UV disinfection for drinking water. It is best used as a pre-treatment step to remove specific contaminants before conventional disinfection. Always consult local water authority guidelines before treating drinking water supplies.
❓ FAQ
Frequently Asked Questions
How do I calculate potassium permanganate dosage for my water tank?
Multiply the tank volume in litres by your target dose in mg/L, then divide by 1,000. For example, a 10,000-litre tank at 5 mg/L needs 10,000 × 5 ÷ 1,000 = 50 grams of KMnO₄. This calculator performs this conversion instantly and adjusts for purity.
What is the safe dose of potassium permanganate for drinking water?
The WHO guideline value for KMnO₄ residual in drinking water is 0.05 mg/L for aesthetic reasons (the pink colour becomes noticeable above this level). Treatment doses of 2–20 mg/L are applied to raw water which is then filtered, flushed, or allowed to naturally reduce before consumption. Never drink water that still shows a pink or purple colour — this indicates excess permanganate is present.
How long should potassium permanganate be in contact with water?
Contact time depends on the application. For iron and manganese oxidation, 15–60 minutes is generally sufficient. For tank disinfection or algae control, allow 1–2 hours minimum. For stubborn hydrogen sulphide problems, up to 4 hours may be needed. After the contact period, flush the tank or filter the water before use.
What does it mean if my water stays purple after treatment?
Persistent purple or violet colour means excess KMnO₄ remains — the permanganate has not been fully consumed by reacting with contaminants. This water must not be consumed. Either flush the tank completely and refill, or add a small amount of sodium thiosulphate solution to neutralise the excess. A faint pink that clears within a few hours is normal and acceptable for pre-treatment applications.
Can I use potassium permanganate in a plastic water tank?
Yes, KMnO₄ is compatible with polyethylene (PE), polypropylene (PP), and fiberglass tanks at standard treatment doses. However, it may stain tank walls with a brown-black manganese dioxide deposit over repeated use. This deposit is harmless but can be removed with a dilute citric acid or ascorbic acid solution. Avoid using KMnO₄ in galvanised steel tanks as it can accelerate corrosion.
Is potassium permanganate the same as chlorine for disinfection?
No — KMnO₄ is a strong oxidant but is not primarily a disinfectant for pathogens. Chlorine (and its derivatives like sodium hypochlorite) is far more effective at killing bacteria and viruses in drinking water. Potassium permanganate excels at removing iron, manganese, H₂S, taste, and odour compounds. The two are often used sequentially: KMnO₄ first to oxidise metals and organics, then chlorine to disinfect. See our Chlorine Dosage Calculator for parallel treatment planning.
How do I dissolve potassium permanganate before adding it to a tank?
Always pre-dissolve KMnO₄ crystals in a bucket of clean water before adding to the main tank. Use roughly 1 litre of water per 10–20 grams of crystals, stir until fully dissolved (the solution will turn deep purple), then pour evenly into the tank while the pump or a mixer is running to ensure uniform distribution. Never add dry crystals directly to a storage tank — this creates high local concentrations that can damage fittings or react unevenly.