Clearing a green pool comes down to killing the algae with a heavy dose of chlorine (shock), then filtering and brushing until the dead algae clears out. Balance the pH first so the shock works, brush every surface, shock hard, and run the pump around the clock, cleaning the filter as it loads up. Light green pools clear in a day or two; a deep-green swamp can take most of a week and several rounds. In Houston heat, algae explodes fast, so move quickly once you see the color turn.
What you'll need
- A test kit
- A stiff pool brush
- A telescoping pole and manual vacuum
- A skimmer net
- Chemical-safe gloves and eye protection
Recommended parts & supplies
- Pool shock (cal-hypo or dichlor) — buy several bags — a green pool needs a heavy dose
- Pool algaecide — helps finish off and prevent regrowth after shocking
- Pool water test kit — to balance pH before shocking
- Pool clarifier or flocculant — helps the filter grab fine dead algae
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Step by step
- 1
Skim, brush, and clear the big debris
Net out leaves and floating debris first so they do not consume your chlorine. Then brush the walls, floor, and steps hard — algae clings to surfaces, and knocking it loose lets the chlorine reach it. Pay attention to shady corners and steps where algae hides. This first scrub makes everything that follows work faster.
- 2
Balance the pH before you shock
Test and adjust pH into the 7.2–7.4 range. Chlorine is far more effective at killing algae when pH is on the low-normal side; shock into high-pH water and much of it is wasted. Take five minutes to correct pH now so the expensive part — the shock — actually does its job.
- 3
Shock the pool hard, at dusk
Add a heavy dose of shock — a green pool needs much more than routine maintenance, often two to four times a normal dose depending on how bad it is. Pre-dissolve cal-hypo in a bucket if the label calls for it, and add it in the evening so the sun does not burn it off before it works. Follow the product directions for your pool volume.
- 4
Run the pump around the clock
Circulation is what carries chlorine to the algae and pulls dead algae to the filter. Run the pump continuously — 24 hours a day — while you are clearing the pool, not just a few hours. Brush again a couple of times a day. The water will often turn from green to cloudy gray or white, which is a good sign: it means the algae is dying.
- 5
Clean the filter as it loads up
All that dead algae clogs your filter fast. Backwash a sand or DE filter, or hose off cartridges, whenever the pressure gauge climbs or flow drops. A clogged filter stalls the whole cleanup, so expect to clean it repeatedly over these few days. A dose of clarifier helps the filter grab the finest particles.
- 6
Re-shock, vacuum, and rebalance
If it is still green the next day, brush and shock again. Once the water goes clear or cloudy-blue, vacuum the settled dead algae off the bottom to waste if you can. Then bring chlorine back to a normal 1–3 ppm, rebalance pH and alkalinity, and add an algaecide to help prevent a repeat. Keep the filter running until the water is fully clear.
When to call a pro
Call a pro if the pool is a black-green swamp you cannot see the bottom of, if it is full of leaves and mud, or if it stays green after two or three rounds of shocking. Severe cases sometimes need a drain and acid wash rather than chemistry, and draining a gunite pool wrong can pop it out of the ground or crack the plaster — a job for someone who knows Houston soil and water tables. If you smell a strong chemical odor, see anyone react to the water, or are unsure how much shock is safe, stop and get help.
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How to Clear a Green Pool (Shock, Filter, and Repeat) — FAQ
How long does it take to clear a green pool?
How much shock does a green pool need?
Should I drain my green pool instead of treating it?
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