Pulled the cover and found a swamp? Don’t panic, and don’t drain it. A green above ground pool can almost always be cleared in 3 to 7 days with the right order of steps: clean out the debris, balance the pH, shock hard, brush, and filter around the clock. Here’s how.

Step 1
Get the debris out

Skim out every leaf you can with a deep bag skimmer on a telescopic pole, including the ones sitting on the floor. Leaves feed algae and soak up chlorine, so every one you remove makes the next steps work faster. Empty the skimmer basket too.

Step 2
Get the filter running

• Top up the water to the middle of the skimmer opening.
• Reconnect the pump and filter, put the drain plugs back, and start it up.
• Clean the filter first: backwash a sand filter, or hose off cartridges or DE grids. A green pool clogs a filter fast, so expect to clean it again and again over the next few days.

Step 3
Test and fix the pH

Test before you add any chlorine. Chlorine loses much of its strength when pH is high, so shocking a pool at pH 8 wastes product. Get pH to 7.2–7.6 and alkalinity to 80–120 ppm first. A good drop kit like the Taylor K-2005 reads chlorine, pH, alkalinity and stabilizer.

Step 4
Shock it hard

A green pool needs much more chlorine than a normal weekly shock. Use liquid chlorine or a granular cal-hypo shock, and follow the label’s dose for algae or green water for your pool’s gallons. Light green may need a double dose, dark green or black a triple dose or more.

• Shock at dusk. Sunlight burns off chlorine, so the overnight hours do the most work.
• Pre-dissolve granular shock in a bucket of pool water. Granules sitting on the floor bleach and weaken the liner.
• Add it in front of a return with the pump running.
• Test the next morning. If chlorine is already gone, the algae used it up. Shock again until chlorine holds overnight. Yellow or pink instead of green? See Yellow, Black or Pink Algae?

Step 5
Brush and filter 24/7

Brush the walls and floor every day with a nylon brush. Never use steel bristles on a vinyl liner. Brushing knocks algae loose so the chlorine can reach it. Keep the pump running around the clock until the water is clear, and clean the filter whenever the pressure climbs 8–10 psi over clean.

The water usually goes from green to cloudy blue-gray. That’s dead algae, and it means it’s working.

Step 6
Clear, vacuum and recheck

• Still cloudy? A dose of clarifier helps the filter catch the fine particles. Don’t overdo it. See Can You Put Too Much Clarifier in a Pool?
• Vacuum the dead algae off the floor with a vacuum head. With a sand filter, vacuum on the Waste setting if there’s a lot of it, so it goes out instead of back through the filter.
• Rebalance pH, alkalinity and stabilizer, and keep free chlorine at 2–4 ppm.
• Keep algae from coming back: if it returns quickly, test for phosphates. A remover like Orenda PR-10,000 takes away the food algae lives on.

Found damage while you were cleaning?

Spring cleanup is when most liner problems show up: a tear at the waterline, brittle vinyl, a liner pulling out of the track, or water that keeps dropping. See 7 Signs Your Above Ground Pool Liner Needs Replacing and Reasons Why Your Pool Is Losing Water. And next fall, a good closing makes for a cleaner opening: Winterizing an Above Ground Pool in New England.

Sources

• CDC: Home Pool and Hot Tub Water Treatment and Testing
• Pool Corporation: How to Balance Pool Water