Quick answer
Green usually means algae (or a sanitizer crash). Test first, brush hard, run the filter nonstop, and raise free chlorine high enough for long enough that the water clears and the walls stop feeling slimy. Guessing with random algaecides first is how green stays green.
What kind of green is it?
- Light / pea soup: often recoverable with brush + shock + filter time.
- Dark / opaque: longer fight; expect multiple days and heavy debris in the filter.
- Black spots on walls: different animal — treat as black algae and be ready to call a pro if it ignores a correct effort.
Test before you dose
You need free chlorine, pH, and ideally CYA. Without CYA context, “how much shock” is a guess. Link the chemistry hubs as they publish; for now, get numbers on paper before you open a bag.
Green-to-clear roadmap
Stage 1 — Prep
Clean baskets, backwash or clean the filter if pressure is high, brush everything, and start continuous filtration.
Stage 2 — Chlorine assault
Use an appropriate shock for your pool type. Skip cal-hypo on many salt systems and some specialty surfaces when the label or system maker says so. Dose, brush, retest — do not dump five products at once.
Stage 3 — Cleanup
As algae dies, water may cloud then clear. Keep brushing, keep filtering, empty the filter as it loads with gunk.
Chlorine pool vs saltwater differences
Salt systems still need free chlorine in the water. A green salt pool often needs manual shock plus fixing why the cell was not keeping up (runtime, salt level, scale on the cell). Don’t assume “salt means maintenance-free.”
What you’ll need
- Test method (strips or liquid kit)
- Brush + continuous filter runtime
- Shock matched to your system
- Patience measured in days, not one evening
Common mistakes
- Algaecide-only “cures” with no free chlorine.
- Short filter runs overnight.
- No brushing (dead algae still sits).
- Mixing chemicals dry or in a bucket.
- Swimming too early because “it looks better.”
When to call a pro
DIY if: you can test, brush, run the filter 24h, and free chlorine holds while color improves.
Call a pro if: equipment fails, black algae persists after a correct high-chlorine effort, or you’re not comfortable handling shock and acid safely.
Key takeaways
- Green is a process, not a single product.
- Test → brush → filter → chlorine → retest.
- System type changes which shock you pick.
- Dead algae still needs physical cleanup.