How to Clean a Green Pool in Los Angeles Without Draining It

A pool goes green in Los Angeles faster than almost anywhere else in the country. Two hot days, a pump on a short summer schedule, a bit of ash or a windstorm full of leaves — and the water you swam in on Friday is a pond by Monday. The good news: you almost never need to drain it. Here is how to clean a green pool in Los Angeles the way our technicians do it, with the doses and timelines we actually use.

Why LA Pools Turn Green So Fast

Algae needs three things: warm water, food and weak chlorine. LA supplies all three.

• Heat. Once water passes about 85°F, algae grows roughly twice as fast. A Valley pool in August sits there for weeks.
• Food. Leaves, pollen, dust from Santa Ana winds and wildfire ash all carry phosphates. Phosphates are fertilizer for algae, and a skimmer basket full of debris is a slow-release feeder.
• Weak chlorine. Sunlight burns off free chlorine within hours if the stabilizer (cyanuric acid) is low. A pump that runs only 4 hours a day in summer never circulates the sanitizer through the whole pool.

Winter has its own trap. The December rains dilute the chemistry, wash dirt in from the deck and fill the pool with debris exactly when most owners have stopped looking at it. That is why calls about green pools in LA spike in December as much as in July.

How Long It Takes, by Water Colour

The colour of the water tells you the dose and the timeline. This is the same scale our crews use on a green-to-clean call. Doses are calcium hypochlorite (cal-hypo, about 65% available chlorine) per 10,000 gallons.

1. Light green, you can see the bottom — early bloom. Double dose: 2 lb. Clears in 24–72 hours.
2. Dark green, bottom barely visible — established algae. Triple dose: 3 lb. Clears in 3–5 days.
3. Black-green, cannot see the steps — swamp, usually dead leaves on the floor. Quadruple dose: 4 lb, repeated. Five to seven days.

What You Need Before You Start

• A test kit or strips that read free chlorine, pH, total alkalinity and, ideally, phosphates.
• Shock: cal-hypo for plaster pools; liquid chlorine (12.5%) for salt or fiberglass.
• A stiff pool brush on a telescopic pole, a leaf rake, and a manual vacuum head with hose.
• Whatever your filter needs: a hose nozzle or spare cartridge, DE powder for DE filters, nothing extra for sand.
• Optional but worth it: a phosphate remover and a quality algaecide for the finish.

Step-by-Step Green Pool Cleanup

1. Skim everything off the surface. Leaves and debris are food. Empty the skimmer and pump baskets too.
2. Brush every surface. Walls, floor, steps, corners, behind the ladder. Algae clings to plaster. Do not vacuum yet.
3. Test and lower pH to 7.2. Chlorine is far more effective at 7.2 than at 7.8. Use muriatic acid or dry acid, then retest.
4. Shock at dusk. Use the dose from the scale above. Add it after sunset so UV does not burn it off before it works. Spread it around the perimeter with the pump running.
5. Run the pump 24 hours a day. Not 8, not 12. Watch the filter pressure: when it rises 8–10 psi above clean, backwash or rinse the cartridge and keep going.
6. Vacuum the dead algae to waste. When the water turns cloudy blue-grey, the algae is dead. Vacuum the floor slowly, sending water to waste if your valve allows, so the dead algae does not clog the filter.
7. Rebalance and finish. Bring free chlorine back to 1–3 ppm, pH to 7.4–7.6, alkalinity to 80–120 ppm. Add algaecide and, if your test showed phosphates above 500 ppb, a phosphate remover.

If the water is still green after 48 hours, retest and shock again. Dark and black pools almost always need a second and sometimes a third round.

Why You Should Not Drain a Los Angeles Pool

Draining feels like a shortcut. In LA it is usually a mistake.

• It may not be allowed. Many water agencies in Los Angeles County limit or require permits for draining pool water, and discharge into the street is regulated. Check your local rules before you pull the plug.
• An empty pool can lift. With a high water table or after rain, hydrostatic pressure can push an empty shell up out of the ground. This is a repair that costs more than any cleanup.
• You pay twice. Refilling 15,000–20,000 gallons at LA rates is not cheap, and you start the chemistry from zero.

A green-to-clean treatment in the existing water works for all but the worst cases. The only time we recommend draining is a true black-water pool with a thick layer of decomposed leaves, and even then we drain only partway.

Filter and Equipment After the Cleanup

• Cartridge filter: hose the pleats from top to bottom, then soak in a filter cleaner overnight. Frayed pleats or a cracked band mean a new cartridge — see filter cleaning.
• DE filter: backwash, open the tank, rinse the grids, and recharge with fresh DE.
• Sand filter: backwash until the sight glass runs clear, then rinse. Sand older than 5–7 years is probably channeled and due for replacement.
• Pump run time: 8–10 hours in summer, at least 6 in winter. A variable-speed pump makes this affordable.
• Saltwater pools: inspect the salt cell for scale; a scaled cell produces far less chlorine than the display suggests.

DIY or Call a Pro in LA?

Doing it yourself is realistic for a light-green pool: in Los Angeles the chemicals usually run $60–150, and it takes two weekends of attention. The risk is a half-finished job — a filter that was not cleaned, phosphates that were never removed — and the pool going green again in July.

A professional green-to-clean visit is a fixed-price job that includes the shock rounds, brushing, vacuuming to waste and a full filter clean, usually over 2–4 days. Call a pro rather than fighting it yourself if:

• the water is black or you cannot see the steps;
• there are yellow or black spots on the plaster — mustard or black algae need a different treatment;
• the filter pressure never drops after cleaning, which points to a filter or pump problem;
• you are selling the home and need it clear on a date.

Pool Care LA handles green-to-clean across Los Angeles and the Valley. Send a photo of the water and we will tell you which step of the scale you are on and what it will cost.