A green pool looks like a big job, but most green pools can be fixed. The cause is almost always the same. Algae grew because the chlorine did not keep up.
This guide explains why pools turn green in North Texas, the steps to clear one, when to call a pro and how to stop it from coming back. It also covers other water problems, such as cloudy water and the types of algae. Chemistry advice here follows CDC guidance and the labels on your products. When a label and this guide differ, follow the label.
Why do pools turn green in North Texas?
Pools turn green when algae grows faster than chlorine can kill it. North Texas gives algae plenty of help: long hot summers, heavy storms, leaves and pollen, and water that is often hard.
Common causes:
| Cause | What happens |
|---|---|
| Low free chlorine | Algae grows when there is not enough sanitizer |
| Heat and sun | Chlorine burns off faster, and warm water helps algae grow |
| Heavy rain and storms | Debris and rain use up chlorine and change the balance (see post-storm algae) |
| Weak filtration | A dirty filter or a short pump run time lets algae spread |
| High pH | Chlorine works less well as pH rises |
| Low or high stabilizer | Too little cyanuric acid lets the sun destroy chlorine, too much can weaken it |
| Dead spots | Corners, steps and behind ladders get little flow |
| A pool that sat unused | Nobody tested the water for days or weeks |
CDC notes that chlorine breaks down quickly. It lists body waste, sweat, dirt and sunlight as things that reduce it. It also says a pH above 8.0 weakens the ability of chlorine to kill germs.
Algae often starts as a few spots you do not notice. By the time the whole pool is green, it has grown for days.
Is it safe to swim in a green pool?
No. Do not swim in green water. A green pool has lost its sanitizer protection, and murky water hides the bottom. If you cannot see the bottom drain, you cannot see a swimmer in trouble.
CDC recommends pH 7.0 to 7.8 and a chlorine concentration of at least 1 ppm in pools. If the pool uses cyanuric acid, CDC says to keep at least 2 ppm. Wait until your tests are in range and the water is clear before anyone swims.
Other safety points:
- Algae is slippery. Steps, ladders and pool edges can become slick. Walk carefully.
- Keep children and pets out of the pool area while you treat it.
- Keep the barrier closed. A green pool is still a drowning risk. See the pool safety section of the handbook.
- Do not swim if you have diarrhea, even in a clear pool. CDC advises this for everyone.
What are the steps to clear a green pool?
Clear a green pool in this order: test, clean the filter, brush, raise chlorine, filter and retest. These are common steps. Follow the label on every product you use.
- Make the area safe. Keep people and pets out. Wear gloves and eye protection when you handle chemicals.
- Test the water. Check free chlorine, pH, total alkalinity and cyanuric acid. A drop test kit is easier to read in green water than test strips. CDC says DPD test kits give the most accurate results and that test strips are less accurate.
- Remove debris. Skim leaves and scoop what you can from the bottom. Debris uses up chlorine.
- Empty the baskets and check the filter. Empty the skimmer and pump baskets. Clean or backwash the filter as its manual directs. A clogged filter cannot clear algae.
- Adjust pH. Chlorine works better when pH is in range. Use the product label for any adjustment.
- Brush every surface. Brush walls, steps, floor, corners and behind ladders. Brushing breaks algae free so chlorine can reach it.
- Raise chlorine with a shock product. Use the label’s dose for algae. See shock. Many owners add shock in the evening, because sunlight burns chlorine off. Follow the label.
- Run the pump and filter. Run them for long hours until the water clears. Watch the pressure gauge, because a filter full of dead algae will clog.
- Clean the filter again. Dead algae loads the filter fast. Clean or backwash again as needed.
- Vacuum and brush again. Remove the dead algae from the floor.
- Retest and repeat. Test each day. If the water is still green or cloudy, repeat the steps. Do not swim until tests are in range and the water is clear.
What safety rules apply to the chemicals?
Pool chemicals cause real injuries, so handle them with care. A CDC release says chemical injuries led to nearly 5,000 emergency room visits in 2012, and that more than a third happened at a home.
CDC safety tips include:
- Read and follow the directions on product labels.
- Wear goggles and masks, as directed, when you handle pool chemicals.
- Secure pool chemicals to protect people and animals.
- Keep young children away when you handle chemicals.
- Never mix different pool chemicals with each other, especially chlorine products with acid.
- Pre-dissolve chemicals only when the label says to.
- Add pool chemical to water, never water to pool chemicals.
If you are not comfortable handling shock or acid, call a pro.
Why does a green pool sometimes stay green?
A green pool stays green when something upstream is wrong. The cause is usually one of these.
| Problem | Sign | Fix |
|---|---|---|
| Filter is clogged or too dirty | Pressure stays high, flow is weak | Clean or backwash, and check the filter |
| Chlorine is being used up too fast | Free chlorine falls soon after dosing | Retest often, brush more, remove debris |
| High chlorine demand from a heavy bloom | Test shows low chlorine again after shock | Repeat the shock steps as the label permits |
| High stabilizer | High cyanuric acid, weak chlorine action | Ask a pro about a partial drain and refill |
| Pump runs too few hours | Water never turns over | Run longer until clear |
| Poor circulation | Algae returns in the same corner | Check returns, brush that area, ask a pro to check flow |
Swim University says free chlorine should sit near 7.5 percent of your stabilizer level. For example, at 40 ppm stabilizer, free chlorine should be about 3 ppm. That rule shows why high stabilizer can keep a pool green even when a basic chlorine test looks fine. Different sources give different guidance, so ask a pro if numbers do not make sense.
When should I call a pro for a green pool?
Call a pro if the water stays green after a few days of correct treatment, if you cannot treat it safely or if your equipment is the problem. A pro can find out why the pool turns green, not just clear it once.
Good reasons to call:
- The pool is dark green or black-green and you have never cleared one.
- The filter will not hold pressure or the pump will not run well.
- You see black spots that do not brush off. See black algae.
- The water clears, then turns green again within days.
- You do not have a good test kit or a safe place to store chemicals.
- You are away, ill or short on time.
Marina Pool Services has a page for algae treatment. It says Marina can get rid of algae fast and get your pool looking good again. It also offers filter cleaning for pools where algae has reached the filter. Marina quotes each job, and it offers free estimates for qualifying services.
If equipment is the cause, Marina can help with filter service and pump repair. For a recurring green pool, weekly pool service keeps the water balanced, so algae never gets a start. For more on this topic, see green pool cleanup in the glossary and the step-by-step guide to clearing a green pool.
What are the types of pool algae?
Pool algae comes in several types, and the color gives a clue about how hard it will be to clear. Green is the most common. Black is the hardest.
| Type | Looks like | Notes |
|---|---|---|
| Green algae | Green water, green film on walls | Most common. Often clears with chlorine, brushing and filtering. |
| Mustard algae | Yellow-brown dust on shady walls | Brushes off but returns. Can cling to gear and swimsuits. |
| Black algae | Dark spots, often on plaster | Roots into surfaces. Often needs a pro. |
| Pink slime | Pink or orange film | Often a bacterial film. Check the plumbing and fittings. |
Treat each type with products made for it, and follow the label. If algae is on a surface and brushes off, you can often handle it. If it grows back in the same spot, ask a pro.
What causes cloudy pool water?
Cloudy water is usually a sign of fine particles or low sanitizer, and it needs the same quick response as green water. See cloudy water in the glossary.
| Cause | What to check | What helps |
|---|---|---|
| Low free chlorine | Test chlorine | Raise chlorine as the label directs |
| Combined chlorine | Test combined chlorine | Treat with shock as the label directs |
| High pH or alkalinity | Test pH and alkalinity | Adjust per the label |
| Dirty or small filter | Check pressure and run time | Clean the filter, run longer |
| Fine dust, pollen, debris | Look at the water and the baskets | Filter longer, brush, vacuum |
| High calcium | Test calcium hardness | Ask a pro. Hard water is common in North Texas |
| After a storm | Debris and runoff | Test, brush, shock if needed |
A clarifier or flocculant can help with fine particles, but they treat the symptom. Find the cause first.
If you cannot see the bottom drain, do not swim. The same rule applies as for green water.
How do I stop a pool from turning green again?
Keep chlorine steady, keep the filter clean and brush every week. These three habits prevent most green pools. Weekly testing is the base.
- Test on a schedule. CDC recommends testing chlorine and pH at least twice per day for public pools. A home pool owner can test less often, but regular testing is the key. Test after storms and heavy use.
- Keep chlorine in range. Know your stabilizer level. Salt pool owners need to check their cell output too.
- Run the pump long enough. Water that does not move turns green.
- Clean baskets and the filter. Check them often during pollen and leaf seasons.
- Brush walls, steps and corners every week.
- Remove debris fast. Leaves use up chlorine.
- Act after storms. Test, brush and clean the baskets.
- Do not let a pool sit. If you travel, ask a pro to keep the water balanced.
Marina’s weekly service covers water balance (chlorine, pH, alkalinity, calcium hardness, conditioner, and salt if applicable), emptying baskets, backwashing filters as needed, and vacuuming and brushing as needed. The water chemistry chart lists target ranges. For local weather patterns, see North Texas pool care and the North Texas pool calendar.
What does a green pool cleanup cost?
Marina Pool Services does not publish prices, and this guide does not estimate what Marina charges. The cost of a cleanup depends on how green the pool is, how much debris there is, what the filter needs and how many visits it takes. Marina quotes each job.
For general background on how local pool companies price work, read the DFW pool service cost guide. It explains what shapes a quote.
A pool in poor shape can also have equipment problems. If your filter or pump is failing, a cleanup alone will not hold. See the pool equipment repair guide.
What should I do about a pool in a vacant home?
A pool at a vacant home can turn green in a week in warm weather. If you are selling, buying or traveling, deal with the water right away.
- Ask a pool pro to restore the water and set up regular service.
- Do not leave the pool without a working barrier.
- Check the filter and pump before you start.
If you are buying a home, the pool checklist for home buyers explains what to look at. Your inspection can also show hidden equipment problems. Marina offers equipment inspection.
Which cities does Marina serve for algae treatment?
Marina Pool Services is based in Grapevine and serves nearby cities. See the Grapevine, Southlake, Colleyville and Keller pages, or the full service areas list.
Next step
If your pool is green or cloudy and you want help, see Marina’s algae treatment page. Call (817) 896-1120 or send a request through the quote form at /contact.
Frequently asked questions
Is it safe to swim in a green pool?
No. Stay out until the water is clear and tests in range. CDC recommends pH 7.0 to 7.8 and at least 1 ppm chlorine in pools, or 2 ppm if the pool uses cyanuric acid. Green water means chlorine is not keeping up, and you also cannot see the bottom or a swimmer in trouble.
Why did my pool turn green overnight?
Algae can bloom fast when chlorine drops. Heat, sunshine, heavy rain, storm debris and a weak filter all use chlorine up. High pH and low stabilizer make it worse. Overnight changes are usually the result of days of falling chlorine that you could not see.
How long does it take to clear a green pool?
It depends on how much algae there is and how well the filter works. A light bloom can clear in a few days. A dark green pool, or one with a weak filter, can take longer and may need repeat treatments. Test the water each day and follow the product label.
Why does my pool turn green after rain?
Rain brings in debris and organic matter, which use up chlorine. Heavy rain can also dilute the water and shift pH and alkalinity. Warm water then helps algae grow. Test the water after a storm, brush the pool and keep the pump running.
Can I just add algaecide?
Algaecide alone rarely fixes a green pool. Sanitizer and filtration do most of the work. Algaecide may help as a supporting product, if the label allows. Check chlorine, pH and the filter first, and follow the product label closely.
Do I need to drain a green pool?
Usually not. Most green pools clear with chlorine, brushing and filtering. A partial drain and refill may help when stabilizer is very high or the water is very old. Ask a pool pro before you drain, because draining can harm some pools.
When should I call a pro for a green pool?
Call when the water stays green after a few days of correct treatment, when the filter will not hold pressure, when you see black spots or when you cannot test or treat the pool safely. Marina Pool Services treats algae in Grapevine and nearby cities.
Pool terms on this page
Sources
- CDC: Home Pool and Hot Tub Water Treatment and Testing
- CDC: Operating Public Pools, Hot Tubs and Splash Pads
- CDC: Pool Chemical Injuries Press Release
- Swim University: Cyanuric Acid
- Marina Pool Services: Algae Treatment
Written by Marina Pool Services and checked against the sources above on October 21, 2026. City rules and product guidance change, so check the linked page before you act. Follow product labels for any pool chemical.
