What this tool is for
Green water is a sequence problem, not a “buy five bottles” problem. Use the stages above to stay in order: test and set up → clean → shock and hold FC → filter → rebalance.
When to open the full guide
- First time dealing with algae
- Water is black-green or you’re unsure about CYA and salt systems
- You need why-not-just-dump-shock detail
Timeline expectations
How long clearing takes depends on the cause of the green and how aggressively you treat it. Realistic windows:
- Light green (algae starting, FC slightly low): 24–48 hours with one shock to breakpoint and steady pump runtime.
- Medium green (clearly green, FC reading zero): 3–5 days with daily shock-and-retest cycles. You may need two shocks if CYA is high and your breakpoint is high.
- Heavy green (peacock or black-green, no visibility at the deep end): 5–14 days. Expect multiple shocks, daily brushing, and possibly a flocculant to drop suspended algae for vacuuming.
- Black-green with dead spots: Often 14+ days. Black algae has a protective coat; brushing and algae-type identification are essential before you’ll see results.
Don’t expect overnight results on anything beyond light green. If you’re at day 7 with no clearing, retest CYA — most “stuck” green pools have a CYA/FC mismatch where your breakpoint is actually higher than the standard table.
When to escalate vs keep going
Keep treating if:
- The water is visibly clearing in any one day (even a small shift)
- FC is dropping as expected (algae consuming chlorine)
- Filter pressure is rising and backwashing returns clear
Stop and reassess if:
- FC holds at the same level two days in a row (you’ve hit your breakpoint — algae is gone or your dose is wrong)
- Filter pressure holds high after backwashing (sand or cartridge may be exhausted)
- Water turns from green to cloudy white but doesn’t clear (could be a different problem — clarifier or flocculant needed)
Common shortcuts that backfire
- Adding algaecide instead of chlorine. Algaecide is a supporting player, not a substitute. Chlorine does the heavy lifting.
- Skipping the brush step. Dead algae clings to walls and floor. Brushing lifts it into the water where chlorine can oxidize it.
- Closing the cover to “wait it out.” Cover traps chlorine off-gas and stops UV decay of algae — the opposite of what you want.
- Backwashing too early. If you backwash before the filter has caught the algae, you just spread it back into the pool.
For a deeper look at the chemistry, see how to clear a green pool and pool shock basics.
After it clears — don’t backslide
The week after a green-pool clear is the highest-risk window for relapse. Algae spores are still in the water and your chlorine demand is just returning to normal. Hold FC at the high end of your target range for at least 7 days, brush daily for the first 3, and keep the pump running longer than usual. If you have a SWG, bump the output percentage up by 10–20% for that week.