Why Your Pool Turned Green
A green pool is algae. It blooms fast — sometimes overnight — when three things line up: warm water, sunlight, and not enough sanitizer (chlorine). One hot weekend with a broken pump or a missed treatment is all it takes.
The good news: most green pools can be cleared in 3-5 days with the right steps. Here's the plan.
Step 1: Test the Water
Before you dump in chemicals, test. You're looking at:
- Free chlorine — almost certainly near zero
- pH — target 7.2-7.6 (high pH makes shock less effective)
- Cyanuric acid (CYA) — high CYA "locks up" your chlorine and is a common hidden cause
If you don't have a reliable test kit, a Taylor K-2006 is the gold standard. Many pool supply stores also test water for free.
Step 2: Balance pH First
Lower your pH to around 7.2 before shocking. Shock works far better in slightly acidic water. If pH is high, your chlorine is fighting with one hand tied behind its back.
Step 3: Shock — Hard
This is where most people under-do it. A light green pool needs a double dose of shock; a dark green or black pool may need triple or quadruple.
- Light green (cloudy): double shock
- Dark green: triple shock
- Black/swamp: quadruple shock + likely a second round
Add shock at dusk (sunlight burns off chlorine) and run the pump 24 hours straight.
Step 4: Brush Everything
Algae clings to walls, steps, and corners. Brush the entire pool — especially shaded areas and behind ladders — so the chlorine can reach it. Brushing daily during the cleanup speeds things up dramatically.
Step 5: Run the Filter Nonstop
Your filter is what physically removes the dead algae. Run it 24/7 during cleanup. Backwash (sand/DE) or clean the cartridge whenever pressure climbs 8-10 PSI above normal — a heavy algae load clogs filters fast.
Step 6: Add Flocculant or Clarifier (Optional)
If the water is still cloudy after the algae dies, a clarifier helps the filter grab fine particles. Flocculant clumps debris to the bottom so you can vacuum it to waste.
Step 7: Re-Test and Balance
Once the water clears:
- Confirm free chlorine is holding at 1-3 ppm
- Rebalance pH, alkalinity, and CYA
- Vacuum any settled debris
How Long Does It Take?
| Pool Condition | Typical Clear-Up Time |
|---|---|
| Light green | 1-2 days |
| Dark green | 3-5 days |
| Black/swamp | 5-7 days (sometimes longer) |
When to Call a Pro
DIY works for most green pools, but call a pool service company if:
- The pool is black or you can't see the bottom step
- It won't clear after a week of treatment
- You suspect an equipment problem (pump not circulating, filter failing)
- You simply don't have time to babysit it for a week
A professional green pool cleanup typically runs $200-$800 depending on severity — often worth it versus buying round after round of chemicals that aren't working.
Find a pool cleaning company near you to handle a stubborn green pool the right way.