Pool Is Green in Dubai? Causes and How to Fix It

When your swimming pool turns green, algae is growing because the free chlorine level has dropped too low to stop it. The fix is the same in almost every case: test the water, correct the pH, brush every surface, shock the pool with enough chlorine to kill the algae, then run and clean the filter until the water is clear.

Keep everyone out of the water until it is clear again. In Dubai's summer heat, a pool can turn green within days if the chlorine runs out.

Why your swimming pool turned green

Algae spores enter every outdoor pool all the time, carried by wind, dust, rain and swimmers. Chlorine normally kills them before they can grow. A pool turns green when something lets the chlorine fall below the level that keeps algae in check, even for a day or two.

These are the most common causes, and a green pool often has more than one:

• Low free chlorine. Free chlorine is the part of the chlorine that is still available to kill germs and algae. If dosing is skipped, the chlorinator runs out, or a salt cell stops working, the level drops and algae starts to grow.
• Strong sun and heat. Sunlight breaks down chlorine quickly. NSW Health's guidance on pool stabiliser says only about 65% of free chlorine remains after one hour of strong sun in an outdoor pool with no stabiliser. Warm water also helps algae grow faster.
• Too much stabiliser. Stabiliser (cyanuric acid, often shortened to CYA) protects chlorine from sunlight, but at high levels it also slows down how well chlorine works. It builds up when you use stabilised tablets or granules, known as trichlor and dichlor.
• High pH. According to the CDC's home pool testing guidance, chlorine's ability to kill germs decreases as pH goes up, especially above 8.0.
• Poor circulation or filtration. A pump that runs too few hours, a clogged filter or blocked baskets leave still water in corners and behind steps, where algae starts first.
• Dust, leaves and rain. Sand, plant debris and garden runoff use up chlorine and can add phosphates, which algae feeds on.

Why Dubai pools go green so quickly

Dubai's summer combines several of these causes at once. The National Center of Meteorology's August climate statistics, reported by Aletihad, give a mean maximum air temperature for August of 40.9°C to 43.2°C. Strong sun burns off chlorine, warm water speeds up algae growth, and dusty winds add debris that uses up the chlorine that is left.

Test the water before you treat a green pool

Testing first tells you why the pool turned green, so you fix the cause rather than just the colour. It also tells you how much chlorine you need, because the right shock dose depends on your stabiliser level.

Use a liquid test kit or take a sample to a pool shop. Test strips are fine for daily checks, but the CDC warns that chlorine readings above 10 ppm can show falsely low or even zero, which is a risk during algae treatment.

Public pool rules in different countries set slightly different limits, so treat these as practical home targets rather than legal standards.

Swimming pool algae: how to tell green, mustard and black types apart

Most green pools have common green algae, but two other types behave differently and need extra effort. A simple brush test helps you tell them apart: brush the affected area and watch what happens.

To spot a pool with algae early, look for a faint green tint, slippery walls or steps, or dull patches in corners and behind ladders. Treating it at this stage is much easier than clearing a fully green pool.

Mustard algae is easy to mistake for sand or pollen. If the "dirt" in the same corner comes back a day after you vacuum it, treat it as mustard algae. It also sticks to brushes, toys and swimwear, so clean everything that touched the water during treatment.

Black algae tends to anchor itself into rough surfaces. A stainless steel brush helps on plaster, but it can damage vinyl liners, fibreglass and some tile finishes, so check your pool surface first.

How to clean a green swimming pool, step by step

Before you start, check the product labels and wear gloves and eye protection. The CDC's pool chemical safety advice warns against letting different pool chemicals mix, and recommends storing them below 35°C, which in Dubai means a shaded, ventilated indoor space rather than an outdoor pump room in direct sun.

1. Remove debris. Skim leaves and empty the skimmer and pump baskets. Debris uses up chlorine and blocks flow.
2. Check the filter and pump. Make sure the pump runs and the pressure gauge looks normal. If the pressure is high, backwash a sand filter or rinse a cartridge filter before you add chemicals.
3. Test and correct the pH. Bring the pH into the 7.0 to 7.8 range before shocking, so the chlorine works at full strength. If it is too high, add a pH reducer (sodium bisulfate, often sold as "pH minus", or muriatic acid), following the label. Add it in small doses with the pump running, then retest after the water has circulated.
4. Brush every surface. Brush the walls, floor, steps and behind ladders. Brushing breaks up the algae film so chlorine can reach it.
5. Shock the pool. Add enough chlorine to raise free chlorine far above the normal level. The product label gives the dose for your pool volume and how green the water is, and a pool with high stabiliser needs more. Add shock in the evening, so the sun does not burn it off before it works. Retest the next morning to confirm the level held.
6. Run the pump continuously. Keep the pump running 24 hours a day until the water is clear. The filter can only remove dead algae that passes through it.
7. Keep the chlorine high. Test at least morning and evening and top up chlorine whenever it falls. Letting it drop lets the surviving algae recover.
8. Brush again daily. Repeat brushing each day, paying extra attention to shaded areas where mustard algae hides.
9. Clean the filter often. Dead algae clogs filters fast. Backwash or rinse whenever the pressure rises, which may be daily at first.
10. Vacuum the debris. Once the water turns from green to grey or blue-cloudy and you can see the floor, vacuum up what has settled.

The water usually changes from green to cloudy grey or blue before it turns clear. That change means the algae has died and the filter now needs time to remove it. For the routine cleaning techniques, such as vacuuming and filter care, see our guide on how to clean a swimming pool.

Do you need an algaecide?

Shock kills the algae; an algaecide is a secondary product that helps stop it growing back. Many are used after the water is clear, as a top-up alongside normal chlorine, not as a replacement for shock. Choose one that matches the label's instructions for your pool, and avoid copper-based types if metal staining is a concern, since copper can turn water green on its own.

Floc or vacuum to waste?

Both are ways to remove large amounts of dead algae faster than the filter can.

• Flocculant (floc) makes fine particles clump together and sink to the floor overnight. You then vacuum them up, ideally on the filter's "waste" setting so the debris goes out of the pool instead of back into the filter. It works best when the pool has a multiport valve with a waste setting.
• Clarifier also clumps particles, but into sizes the filter can catch, so it works more slowly and needs no vacuuming to waste.
• Vacuum to waste sends water and debris out of the pool, so you will need to top up the water afterwards. This also helps lower stabiliser and phosphate levels.

Zodiac's guidance suggests adding a floc or clarifier the day after shocking if you still cannot see the bottom. If your pool has a cartridge filter and no waste valve, a clarifier is usually the simpler choice.

How to know the pool is fully clear

Clear-looking water is not enough on its own. Small amounts of algae can survive on walls and in the filter, and they grow back within days if you stop treatment too early.

You can treat the pool as cleared when all of these are true:

• The water is clear and you can see the main drain.
• No green, yellow or black film appears when you brush.
• The chlorine level you add in the evening is still mostly there the next morning.

The overnight test matters most. If chlorine keeps disappearing overnight with no sun on the water, something in the pool, usually remaining algae, is still using it up. Once all three are true, let the chlorine fall back to your normal range before anyone swims.

Pool still green after shock? The usual reasons

If you shocked the pool and it is still green a day or two later, one of these is usually the reason.

Not enough chlorine for the stabiliser level

This is the most common cause in sunny climates. Stabiliser holds chlorine in a weaker form, so a dose that clears a low-stabiliser pool may barely touch one with a high reading. NSW Health notes that stabiliser is not used up by the pool and only leaves through splashing or backwashing.

So the only quick way to lower a very high stabiliser reading is to replace part of the water with fresh water. Do not fully drain an in-ground pool without professional advice, because emptying it can damage the shell, and check your community's rules on where pool water can be discharged.

pH too high

Large doses of calcium hypochlorite or liquid chlorine can push pH up. If the pH climbs above 7.8 during treatment, chlorine loses strength. Retest and correct the pH during treatment, not only before it.

Filter or circulation problems

A dirty filter, a short pump schedule or a blocked return jet leaves dead zones where algae survives. Check that water is moving in every part of the pool and clean the filter more often during treatment.

Metals, not algae

If the water turned green or teal right after you shocked it, and the walls do not feel slimy, the cause may be copper or another metal. Zodiac explains that metals such as copper oxidise when chlorine levels are high, which can turn water green. Sources include copper-based algaecides and corroding pipes or heat exchangers.

Adding more shock will not fix a metal problem. Test for metals, use a metal remover or sequestrant as directed, and check pool heater or chiller manuals before shocking, as some manufacturers advise bypassing the heater during heavy chlorination.

Phosphates

Phosphates do not cause algae on their own, but they feed it. If algae keeps coming back despite good chlorine, test phosphates and use a phosphate remover if the level is high.

Why your pool turns green after rain or a dust storm

A pool can turn green within a day or two after rain or a sandstorm, even if it was clear before. Rain dilutes the chlorine, and both rain and wind wash in dust, leaves, soil and garden fertiliser. All of this uses up chlorine and can add phosphates.

Rain is rare in Dubai, so many pool owners are caught off guard when it arrives. Dust is a more regular problem, especially in villas with sandy plots or open land nearby.

After a storm or heavy rain:

1. Skim debris and empty the baskets.
2. Test free chlorine and pH the same day.
3. Add chlorine to bring the level back up, and correct the pH.
4. Run the pump for longer than usual and brush the floor to lift settled dust.
5. Clean the filter once the pressure rises.

Acting the same day usually prevents a full algae bloom. Plants and lawns that drain towards the pool make the problem worse, which is worth considering when planning pool landscaping.

How to get pool water clear after the green is gone

Cloudy water after an algae treatment usually means the filter has not yet removed all the dead algae and fine particles. It is a normal stage, not a sign the treatment failed.

To clear cloudy swimming pool water:

• Keep the pump running until the water is clear. Most of the clearing work is done by the filter.
• Clean the filter whenever the pressure rises. A clogged filter cannot hold more debris.
• Check pH and chlorine. High pH and low chlorine can both cause cloudiness on their own.
• Use a clarifier if the cloudiness lasts more than a couple of days with a clean filter.

If the water stays cloudy for a week with good chemistry and a clean filter, the filter may be worn out or too small for the pool. Old sand that has clumped together, or a torn cartridge, lets fine particles pass straight through.

How to stop pool algae coming back in a Dubai summer

Never let free chlorine drop to zero, and keep the water moving. Prevention is much easier than clearing a green pool.

• Test more often in summer. The CDC recommends testing chlorine and pH at least twice a day for home pools. Even if you test less often, increase checks from May to September and after storms.
• Keep stabiliser in a sensible range. If you use trichlor tablets, the stabiliser level rises over time. Test it monthly and switch to an unstabilised chlorine if it climbs too high.
• Add chlorine in the evening. Chlorine added at night works for hours before the sun starts breaking it down.
• Run the pump long enough. Longer run times in summer help the filter keep up with dust and debris.
• Brush weekly. Focus on steps, corners and shaded walls, where algae starts first.
• Plan for travel. Arrange for someone to test and dose the pool while you are away, because summer heat can turn it green within days.

A full routine with daily, weekly and monthly tasks is in our pool maintenance checklist for Dubai.

When to call a pool professional in Dubai

You can clear a lightly green pool yourself with a test kit, a brush, chlorine and patience. Calling a professional makes sense when:

• the pool is dark green and you cannot see the floor;
• it is still green after several days of high chlorine;
• you suspect metals, black algae or a failing filter;
• the stabiliser is very high and part of the water needs replacing.

NAM Landscaping's in-house team offers pool cleaning in Dubai, with a free site visit and a written, itemised quote before work starts. If you would rather avoid green water altogether, regular pool maintenance visits include routine chemicals and a photo report sent to your WhatsApp after every visit.

If algae keeps returning because of rough, worn plaster or failing equipment, the long-term fix may be resurfacing or an equipment upgrade, covered in our guide to swimming pool construction and renovation costs in Dubai.