A green pool is dramatic, but almost always fixable in 3–5 days with the right method. We use the SLAM method — Shock Level And Maintain — the same protocol recommended by Trouble Free Pool (TFP) and most pros.
Before you start: test everything
- Free chlorine: will be near zero
- CYA: critical — determines your shock target
- pH: lower to 7.2 before starting (chlorine works faster in slightly acidic water)
- Filter condition: clean it first — a clogged filter can't help you
The SLAM protocol
- Raise free chlorine to the SLAM level for your CYA (see table).
- Test FC every 2–4 hours during the day. Re-dose to maintain SLAM level.
- Brush the entire pool daily, especially corners and steps.
- Run the filter 24/7.
- Vacuum dead algae to waste as it drops.
- Continue until: CC < 0.5 ppm, overnight FC loss < 1 ppm, water is crystal clear.
SLAM target by CYA
| CYA (ppm) | Maintain FC at (ppm) |
|---|---|
| 30 | 12 |
| 40 | 16 |
| 50 | 20 |
| 60 | 24 |
| 80 | 31 |
Timeline
- Day 1: Pool turns from green to cloudy gray. You're winning.
- Day 2–3: Cloudy gets lighter. Dead algae on the bottom.
- Day 3–5: Water clears. Pass the three SLAM completion tests.
Don't fall for algaecide
“Quick algaecide” products work on light, early algae — but a fully green pool needs real chlorine levels. Algaecide with a SLAM-level chlorine pool just foams up and wastes money.
Prevention: why it happened
Green algae shows up when free chlorine drops below the minimum FC/CYA ratio for too long. Common causes: CYA crept up past 80 ppm, tablet feeder ran out during a vacation, salt cell stopped producing, or heavy storm diluted everything below threshold. Find and fix the root cause or you'll be doing this again in 3 weeks.