Why Pool Water Turns Green and How to Fix It

You walk out to the backyard and the pool that was clear last week looks like a pond. It happens to Las Vegas homeowners every year, and it usually happens faster than people expect. The good news is that green water is almost always fixable once you know what caused it.

What actually turns pool water green

In nearly every case, the green is algae. Algae spores blow into every pool all the time. When your chlorine is at a healthy level, they die before they can grow. When it drops, they bloom, and a clear pool can turn cloudy green in a day or two.

The usual triggers are:

• Low or ineffective chlorine. Not enough sanitizer, or chlorine that is present but not working.
• High pH. Chlorine loses much of its strength when pH climbs well above the ideal range of about 7.4 to 7.6.
• Poor circulation or a dirty filter. Water that is not moving and filtering lets algae settle in, especially in corners and behind ladders.
• Debris and dust. Leaves, dirt and organic matter use up chlorine and feed algae.
• Metals in the water. Copper can give water a green or blue-green tint without any algae at all. This is less common, but it is worth ruling out if the water stays tinted after a thorough treatment.

Why Las Vegas pools go green so fast

Our climate gives algae a few advantages.

Sun and heat. Strong desert sun breaks down chlorine quickly, and in summer the water gets warm, which algae love. A pool that held steady in April can lose its protection in a hot week.

Too much stabilizer. Cyanuric acid (CYA) shields chlorine from the sun, which helps here. But if you rely on chlorine tablets, CYA keeps building up. At high levels it makes your chlorine sluggish, so you can have a reading that looks fine and still grow algae.

Hard water and evaporation. Las Vegas tap water is hard, and evaporation is high. As water evaporates and gets topped off, minerals concentrate and the chemistry becomes harder to keep balanced. High pH and scale are common results.

Wind, dust and storms. Desert wind carries dust and debris into backyard pools year-round. Summer monsoon storms can add even more, and a single storm can overwhelm a pool that was already running low on chlorine.

Travel and heat waves. Many people leave town in summer. A week or two without checking the pool is plenty of time for algae to take over.

How to fix a green pool

This is the basic process for a light to moderate bloom. Always follow the label directions on any chemical, and never mix chemicals together.

• Remove debris. Skim the surface and clear the baskets so the filter can move water freely.
• Test the water. Check pH, chlorine, alkalinity and CYA. A good test kit or a trip to a pool store for a water sample will tell you what you are dealing with.
• Adjust pH first. Bring pH down toward the 7.4 to 7.6 range so the chlorine you add can do its job.
• Brush every surface. Walls, steps and floor. Brushing breaks up algae so the chemicals can reach it.
• Shock the pool. Add pool shock at the dose on the label, ideally in the evening so the sun does not burn it off. A bad bloom can take more than one dose.
• Run the pump around the clock. Keep the water circulating and filtering while the pool recovers.
• Clean the filter. Dead algae clogs the filter quickly. Backwash or rinse cartridges as often as needed, and a deep clean of the media may be required.
• Retest and repeat. Keep chlorine at a healthy level until the water is clear and holds its reading overnight. Then vacuum up any settled debris.

If the water is cloudy but no longer green, a clarifier can help the filter catch the fine particles that remain.

Common mistakes that make it worse

• Adding shock without correcting pH first.
• Skipping the brushing.
• Shutting the pump off to save energy while the pool is green.
• Ignoring a dirty filter.
• Draining the pool right away. It is rarely necessary and can be hard on the pool surface and equipment.

How to keep it from coming back

Green pools are mostly a consistency problem. Test the water weekly, keep the filter clean, brush regularly, and run the pump long enough each day to turn over the water. Check CYA a few times a year, especially if you use tablets. In summer, check more often, since heat and sun use up chlorine faster.

If the pump is noisy, leaking or losing prime, get it looked at early. Weak circulation is one of the biggest hidden causes of algae, and pump and motor repair starts with a diagnosis and a quote before any work is done.

Many homeowners find it easier to hand off the routine. With weekly pool service, a tech skims, brushes, balances the water and checks the filter every week. You get a text with the chemical readings after each visit, so you can see the water stay on track. Blue Basin Pool Care provides weekly pool service in Las Vegas and across the valley, and weekly service starts from $120 a month, with the exact rate confirmed before the first visit.

When to call a pro

Call for help if the water is dark green or black, you cannot see the bottom, the pool has been green for weeks, or you have treated it and it keeps coming back. The cause may be a circulation problem, a filter issue or a chemistry imbalance that is hard to spot without the right testing.

Our green pool cleanup takes a pool from green to swim-ready, usually within a few days, and starts from $250. We give a firm quote after seeing the pool. You do not need to be home, since we only need gate access.

Ready for clear water?

Blue Basin Pool Care has served the Las Vegas valley for 11 years, including Henderson, Summerlin, North Las Vegas, Centennial Hills and Southern Highlands. Book online or call (702) 555-0194, and we will get your pool back to blue.