Perhaps we missed the signs, the water's been cloudy—and today we walk outside with the expectation of an easy clean: only to find the pool has turned overnight!
Whether your water is light green, cloudy, or starting to swamp, you can restore it for a crystal-clear swim within 24 to 48 hours (with the right approach!)
What Happened!?
Green pool water is almost always a sign that algae has found an opportunity in chemistry or circulation weak spots. Common triggers include:
- Hot temperatures
- Excessive sunlight
- Chemical imbalances
- Heavy pool usage
- Organic debris
- Dirty filters
- .. and more!
The moment your levels fall, algae moves in fast.
That’s why a green pool can appear in a single day, but you can turn it around just as quickly.
What You’ll Need (Poolzilla Essentials)
To clear a green pool fast, make sure you have:
-
Water test kit
We recommend a more extensive kit, rather than test strips, in this event!
- Liquid chlorine
You're gonna need that boost afterwards!
- Pool Brush
- Skimmer Net
-
Clarifier or Flocculant
Depending on cloudiness
Step 1: Test & Balance.
Before you overrun the pool with shock, check and balance:
-
Free and total chlorine
-
pH
-
Total alkalinity
-
Calcium hardness
-
Cyanuric acid (CYA)
- Salt level (If applicable)
If accessible, have your pool tested for phosphate levels ahead of time!
Most green-pools follow this pattern:
- Chlorine depletes, pH rises, OR CYA drops →
- Chlorine loses power or disappears →
- Algae takes advantage →
- Water turns green
Step 2: Remove Debris & Brush Everywhere.
Any debris within the water can be contributing to why algae has made itself at home.
- Brush walls, steps, and the floor thoroughly, ensuring you're scrubbing at every nook and cranny
- Scoop out leaves or any other organic floating debris
Brushing sounds like a chore, but this step is crucial to knocking all that algae into suspension, where chemicals can attack it effectively. Allow the water some time to circulate your rebalanced chemicals before tackling step three.
Step 3: Shock the Pool.
You will want to read the packaging thoroughly, as instructions may vary between brands. Most will recommend that you use a set amount per 10,000 gallons. In extreme situations, you may require double or even triple the amount!
Consult with a pool pro if you're unsure of the proper dosage in your case.
We'll provide the basics:
- Never pour shock directly into the water; pre-mix in a clean bucket of warm water, 3/4 of the way full.
- Verify your pool equipment is running.
- When pouring, work around the entire length and width of the pool.
Poolzilla tip: Never mix multiple types or brands of shock at the same time! Even if the ingredients reflect the contents as the same, it's better to be safe than sorry.
Step 4: Brush Again & Keep Circulating.
Give the pool another brush; this will help now to loosen any clinging algae and circulate the treatment to ensure your liner and pool finish maintain their integrity against shock staining! Your pump and filter are doing the heavy lifting now; allow them to run for at least 8 to 12 hours.
Step 5: Confirm Chlorine Is Still High Enough
After the initial shock, your chlorine should still be elevated.
If chlorine has already depleted (usually due to high algae load), that means the shock got “eaten up” doing its job.
If algae is still visible, or even worsening, and FC is low → You might need to shock again.
Pro tip: Backwash sand or DE filters as PSI rises, clean cartridge as needed.
Step 6: After 24 Hours, Add Algaecide
You only want to add algaecide when:
- pH is between 7.2 to 7.6
- Chlorine is still elevated, but not sky-high (algaecide loses effectiveness if FC is extremely high)
If the water turns lightly cloudy:
Use a clarifier to help your filter trap tiny particles.
If the water is milky or heavily cloudy:
Use a flocculant to drop debris to the bottom overnight, then vacuum! These work effectively, but can create a headache if used improperly. Follow all instructions provided.
If the water is still very green:
If you find yourself with a pool only getting greener, it might be time to call the pros! High phosphate levels encourage algae growth, possible equipment or pool leaks, circulation issues, or metals in the water can be the culprit!
Once your pool is clear again, it's time for a little check-in!
Your filter traps a massive amount of dead algae, fine debris, and organics throughout this process, and to keep your pool from turning green again:
-
Cartridge Filters:
Rinse thoroughly with a hose or use a cartridge cleaner.
Replace if there is visible damage, pleats are frayed, collapsed, or no longer holding shape. -
Sand Filters:
Perform a long backwash and rinse cycle.
Replace sand every 4–5 years, or sooner if it clumps or channels. -
DE Filters:
Backwash and recharge with fresh DE.
Replace grids if torn or misshapen.
Final Thoughts:
Strong shock, balanced water, and reliable filtration work together to turn your pool around in a single day or two.
Keeping fresh, effective chemicals and a healthy filter system ensures your pool stays crystal-clear long after the algae is gone. Check out our guidelines for easy pool care!
.. and if you need replacement filters, algaecide, shock, or any of the chemicals mentioned above, Poolzilla has you covered.