Pool Care Guide · For pool owners & operators
How much chlorine does a swimming pool need? The complete guide to clear, safe, algae-free water
Correct chlorine doses, why pools turn green, how to clear a green pool fast, and the simple daily routine that keeps water sparkling all season.
⏱ 12 min read · 🏊 For home, hotel & club pools · 🧪 Test daily
Quick answer: keep free chlorine at 1–3 ppm (2–4 ppm for busy hotel and club pools) and pH at 7.2–7.6. With TCCA 90, about 1.1 g per 1,000 litres raises chlorine by 1 ppm. Most outdoor pools in India need roughly 1–2 g of TCCA per 1,000 litres per day in summer. Always test first, then dose.
In this guide
1. Ideal pool water numbers · 2. Find your pool volume · 3. Chlorine dose and timing · 4. Why TCCA · 5. What algae is · 6. Why pools turn green · 7. Clearing a green pool · 8. Still green after TCCA? · 9. Daily, weekly and monthly routine
1. The ideal numbers for clean pool water
Chlorine is only half the story. Chlorine works well only when the rest of the water chemistry is in range. Test these regularly with a pH and chlorine test kit.
| Parameter | Ideal range | Test how often | Why it matters |
|---|---|---|---|
| Free chlorine (FC) | 1–3 ppm (home) 2–4 ppm (hotel, club, school) |
Daily (twice a day for busy pools) | Kills germs and algae. Below 1 ppm, algae can start growing within a day in hot weather. |
| pH | 7.2–7.6 | Daily | At high pH chlorine becomes weak. At low pH water stings eyes and corrodes fittings. |
| Total alkalinity (TA) | 80–120 ppm | Weekly | Keeps pH steady. Low TA makes pH swing up and down. |
| Stabiliser (cyanuric acid, CYA) | 30–50 ppm | Every 2 weeks | Protects chlorine from sunlight. Too much (above 80–100 ppm) makes chlorine slow and weak. |
| Calcium hardness | 200–400 ppm | Monthly | Too low damages plaster and grout; too high causes scale and cloudy water. |
| Combined chlorine | Below 0.2 ppm | Weekly | Used-up chlorine that causes the strong "pool smell" and red eyes. Fix it with a shock dose. |
Remember: 1 ppm (part per million) = 1 gram per 1,000 litres (1 cubic metre) of water. This makes every dose calculation easy.
2. First, find your pool volume
Every dose depends on how much water you have. Measure in metres and use the average depth (shallow end + deep end ÷ 2).
| Pool shape | Formula (litres) | Example |
|---|---|---|
| Rectangle / square | Length × Width × Average depth × 1,000 | 10 m × 5 m × 1.5 m = 75,000 L (75 m³) |
| Round | Diameter × Diameter × Average depth × 785 | 6 m × 6 m × 1.2 m × 785 = 33,900 L |
| Oval | Length × Width × Average depth × 785 | 8 m × 4 m × 1.4 m × 785 = 35,170 L |
3. How much chlorine to add, and when
Raising chlorine by 1 ppm
| Chlorine source | Available chlorine | To raise 1,000 L by 1 ppm | For a 75,000 L pool (+1 ppm) |
|---|---|---|---|
| TCCA 90 (granules / tablets) | 90% | ≈ 1.1 g | ≈ 83 g |
| Sodium hypochlorite 10–12% (liquid) | 10–12% | ≈ 8–10 ml | ≈ 650–750 ml |
| Bleaching powder | 30–35% | ≈ 3 g | ≈ 230 g |
Daily maintenance dose with TCCA 90
- Normal use: about 1–2 g of TCCA per 1,000 L per day for an outdoor pool in summer. A 75,000 L pool usually needs 75–150 g a day.
- Busy pools (hotels, clubs, schools, after a party): add more, as each swimmer uses up chlorine. Test twice a day and dose to keep 2–4 ppm.
- Winter / covered pools: chlorine loss is slower, so you may need only half the summer dose.
- Let the test kit decide. If morning chlorine is below 1 ppm, increase the dose. If it is above 3–4 ppm, reduce it.
Best practice: how and when to add chlorine
Test first. Check free chlorine and pH every morning before opening the pool. Correct pH first; chlorine works best at pH 7.2–7.6.
Add in the evening. Dose after swimmers leave, ideally after sunset. Sunlight destroys chlorine, so chlorine added at night works all night on germs and algae.
Keep the pump running. Always add chemicals with the filter pump ON so they mix through the whole pool. Run it at least 2–3 hours after dosing.
Use a floater or feeder for tablets. TCCA tablets in a floating dispenser or automatic feeder release chlorine slowly and keep levels steady. Never put tablets directly in the skimmer if your pump has metal parts.
Pre-dissolve granules. Dissolve TCCA granules in a plastic bucket of pool water (add chemical to water, never water to chemical) and pour slowly along the deep end. Do not throw dry granules on vinyl or painted surfaces; they can bleach.
Wait before swimming. After a normal dose, wait 1–2 hours. After a shock dose, wait until free chlorine falls back to 3–4 ppm (usually the next morning).
Safety first: never mix TCCA with bleaching powder, calcium hypochlorite or any other chemical, either dry or in the same bucket. The mixture can catch fire or explode. Add different chemicals separately, at least 1 hour apart. Wear gloves and goggles, and store TCCA in a cool, dry, closed container away from children.
4. Why TCCA 90 is the most practical chlorine for pools
Highest strength
90% available chlorine, compared with 30–35% in bleaching powder and 10–12% in liquid hypochlorite. You buy, store and handle far less product.
Sun-protected (stabilised)
TCCA contains its own stabiliser (cyanuric acid), which protects chlorine from sunlight. Unstabilised chlorine can lose most of its strength in a few hours of strong Indian sun.
Slow and steady
Tablets and granules dissolve slowly and keep chlorine at a steady level all day, instead of a high peak and a quick drop.
No calcium, less cloudiness
Unlike bleaching powder, TCCA does not add calcium or insoluble residue, so water stays clearer and there is less scaling on tiles and filters.
Long shelf life
Stays strong for a long time when stored dry and closed, unlike liquid hypochlorite, which slowly loses strength in storage.
Easy for staff
Measured tablets or granules are simple for pool attendants to dose correctly every day.
The one thing to watch: because TCCA adds stabiliser every day, CYA slowly builds up (roughly 0.6 ppm CYA for every 1 ppm of chlorine added). Test CYA every 2 weeks. If it goes above 80–100 ppm, replace part of the water, and use unstabilised chlorine (liquid hypochlorite or bleaching powder) for shock doses. TCCA also lowers pH a little over time, so check pH daily.
5. What is algae?
Algae are tiny plant-like organisms that float in the air and arrive in your pool with wind, dust, rain, leaves and even swimwear. Like plants, they grow using sunlight, warmth and nutrients. In warm water with too little chlorine, a few cells can multiply into a green pool in just 24–48 hours.
Green algae (most common)
Floats in the water or forms a slimy green film on walls and steps. Turns water hazy green. Easiest to remove.
Yellow / mustard algae
Yellow-brown powdery patches in shaded corners. Brushes off easily but comes back quickly; needs a strong shock and cleaning of all equipment.
Black algae
Small black-blue spots with "roots" in plaster and grout. The hardest type: needs hard brushing with a steel brush (not on vinyl), spot treatment and repeated shock.
6. Why does a pool turn green? The main factors
| Cause | What happens | Fix |
|---|---|---|
| Low chlorine | Chlorine falls below 1 ppm (heat, sunlight, many swimmers, rain), and algae starts growing. | Test daily; keep 1–3 ppm; dose in the evening. |
| High pH (above 7.8) | At pH 8, chlorine has only about a quarter of its strength. You add chlorine but it does little. | Bring pH to 7.2–7.6 before chlorinating. |
| Too much stabiliser (CYA) | After months of TCCA only, CYA becomes so high that chlorine is "locked" and works very slowly. | Test CYA; replace part of the water if above 80–100 ppm. |
| Poor filtration | Pump runs too little, the filter is dirty or the sand is old, so algae and dirt are not removed. | Run the pump 8–12 hours a day; backwash regularly; change filter sand every 3–5 years. |
| Poor circulation / dead spots | Corners, steps and behind ladders get little water flow, so algae grows there first. | Brush these areas daily; point return jets to stir the water. |
| Nutrients | Leaves, dust, bird droppings, fertiliser and rain run-off add phosphates and nitrates that feed algae. | Skim daily; cover the pool; keep garden water and soil out. |
| Heat and sunlight | Hot weather speeds up algae growth and burns off chlorine faster. | Increase dosing in summer; test twice a day. |
| Heavy bathing load | Sweat, sunscreen and body oils use up chlorine quickly. | Shower before swimming; dose extra after busy days. |
| Rain | Rain dilutes chlorine, lowers pH and washes in dirt and spores. | Test and shock after heavy rain. |
7. How to clear a green pool: step by step
This method works for most green pools in 2–5 days. Keep the pool closed to swimmers until the water is clear and chlorine is back to normal.
Remove debris. Take out leaves and dirt with a leaf net. Empty skimmer and pump baskets.
Run the filter non-stop. Clean or backwash the filter, then run the pump 24 hours a day until the water is clear.
Test and correct pH. Bring pH to 7.2–7.4. Chlorine is much stronger at this level. If alkalinity is low, raise it first so pH stays steady.
Brush everything. Brush walls, floor, steps and corners hard with a pool brush. This breaks the algae's protective layer so chlorine can reach it. Brush every day during treatment.
Shock with chlorine in the evening. Raise free chlorine to 10–20 ppm (higher for dark green water). If your stabiliser is high, use liquid sodium hypochlorite or pre-dissolved bleaching powder for the shock, not more TCCA. Example: for 75,000 L, raising chlorine by 15 ppm needs about 11 litres of 10% hypochlorite.
Keep chlorine high. Test morning and evening. Top up chlorine whenever it falls below the shock level, until the water turns from green to cloudy blue and then clear.
Add algaecide if needed. For stubborn algae, add copper sulphate algaecide as per the label, after the shock. Do not overdose; too much copper can stain plaster and turn hair green.
Clear the dead algae. Dead algae makes water cloudy grey-blue. Use pool floc in the evening: switch the pump off overnight, let the dirt settle, then vacuum it out slowly to waste (not back through the filter).
Backwash and rebalance. Backwash the filter, then check pH, alkalinity and chlorine. Open the pool when chlorine is 1–3 ppm and pH 7.2–7.6.
How do you know the algae is fully gone? Do an overnight test: check chlorine after sunset and again before sunrise. If it drops by less than 1 ppm overnight, the water is clear and no green or dust-like particles remain, the algae is dead. If chlorine keeps disappearing, algae is still alive somewhere. Keep brushing and dosing.
8. "I added a lot of TCCA, but my pool is still green." Why?
This is the most common question we get from pool owners. Adding more TCCA rarely fixes it. One of these is usually the real reason:
| Reason | How to check | What to do |
|---|---|---|
| Stabiliser (CYA) is too high | CYA test shows above 80–100 ppm, often after many months of TCCA only. | Replace 30–50% of the water with fresh water, then shock with liquid hypochlorite or bleaching powder instead of TCCA. |
| pH is wrong | pH above 7.8 (weak chlorine) or below 7.0 (TCCA lowers pH and alkalinity over time). | Correct alkalinity first, then pH to 7.2–7.4, then shock again. |
| Not enough chlorine for the algae | Chlorine reads 0–1 ppm a few hours after dosing; algae is eating it all up. | Shock to 10–20 ppm in one go in the evening, and keep it there until clear. Small daily doses cannot beat a full bloom. |
| Filter not working | Low flow, pump running only a few hours, high pressure gauge, or old clumped sand. | Backwash, run the pump 24 hours, check sand; replace if it is more than 3–5 years old. |
| No brushing | Slimy walls and corners. | Brush the whole pool daily during treatment. |
| It is not algae, it is metal | Water is clear but tinted green (not cloudy), often after adding copper sulphate or using borewell water with iron/copper. Shock makes it worse. | Stop copper algaecide; use a metal sequestrant; partial water change. Chlorine will not fix metal colour. |
| Chlorine added in daytime | Strong sun burns off chlorine before it can work, especially with unstabilised products. | Dose in the evening with the pump running. |
| Dead algae left in the water | Water turns from green to dull grey-blue and cloudy, but chlorine now holds. | Algae is dead. Use floc, vacuum to waste and backwash. |
9. What keeps a pool clean: the daily, weekly and monthly routine
Clean pools are not made by chemicals alone. They come from three things working together: correct chemistry, good filtration and circulation, and regular cleaning. Weakness in any one of them lets algae in.
Daily
- Test free chlorine and pH (morning before opening; again in the evening for busy pools).
- Skim leaves and floating dirt; empty skimmer baskets.
- Run the filter pump 8–12 hours (longer in summer or after heavy use).
- Keep chlorine at 1–3 ppm (2–4 ppm for commercial pools); dose in the evening.
- Ask swimmers to shower before entering; no oils or heavy creams in the pool.
- Keep a simple logbook: date, chlorine, pH, chemicals added, pump hours.
Weekly
- Brush walls, floor, steps and corners.
- Vacuum the pool floor.
- Backwash the sand filter when the pressure gauge rises about 0.5–0.7 kg/cm² (7–10 psi) above the clean reading.
- Shock once a week, or after a party, heavy rain or many swimmers.
- Test total alkalinity and combined chlorine.
- Clean the waterline tiles to remove oil and scale.
Every 2–4 weeks / monthly
- Test stabiliser (CYA) and calcium hardness.
- Check pump, valves, and the multiport valve for leaks.
- Check water level; top up with fresh water (this also lowers CYA).
- Clean the pump strainer and check the filter sand.
- Once a season, have the filter sand inspected; replace every 3–5 years.
Pool care products from Cleansol
Daily chlorine
TCCA 90 Chlorine Granules
Stabilised 90% chlorine for steady, long-lasting disinfection.
Shop now →
Shock dose
Sodium Hypochlorite 10–12%
Fast liquid chlorine for shocking green pools; adds no stabiliser.
Shop now →
Testing
Pool pH & Chlorine Test Kit
Check chlorine and pH in a minute, every day.
Shop now →
Algae control
Copper Sulphate for Pools
Algaecide to prevent and treat stubborn green algae.
Shop now →
Clear cloudy water
Pool Floc Powder
Settles dead algae and fine dirt overnight for easy vacuuming.
Shop now →
Cleaning tool
Pool Wall Brush
Brush walls, steps and corners where algae starts.
Shop now →See all pool chemicals, equipment and safety products →
Frequently asked questions
Pool still green or cloudy?
Send us your pool size, a photo of the water and your latest chlorine and pH readings on WhatsApp. Our technical team will suggest the right treatment and quantities.
Chat on WhatsApp Shop pool careSafety: the doses in this guide are general guidance for typical pools. Always test your water, follow the product label, and adjust for your pool. Keep pool chemicals in their original containers, dry and cool, out of reach of children. Never mix different pool chemicals.