How to Get Rid of Algae Growth in a Pool

Algae growth isn’t a mystery—it’s a sign that your sanitiser, balance, filtration, or circulation has fallen behind due to weather and debris. The fix is a sequence, not a single product. Follow Pool Life’s step-by-step plan to kill the bloom fast, clear the cloudiness, and stop it from coming back.

AlgaeAlgae growth – Quick diagnosis (60 seconds) 

• Colour: light/pea green (common), mustard/yellow (shady walls/steps), or black spot (dark dots with roots).
• Equipment: baskets full? Filter pressure +8–10 psi above clean? Pump fully primed?
• Chemistry: pH high? Is the Free Chlorine (FC) low for your stabiliser (CYA) level?

If you see ongoing water loss, do a bucket test first—leaks won’t be solved with chemicals.

What you’ll need

• Drop-test kit or photometer (FC, pH, TA, CH, CYA; salt if applicable)
• Liquid chlorine (sodium hypochlorite) for shocking
• Pool acid (to set pH)
• Stiff algae brush (plaster) or soft brush (fibreglass/vinyl)
• Manual vacuum & hose (even if you own a robot)
• Clarifier or flocculant (optional; use one, not both)
• Filter cleaner; spare baskets/O-rings

Safety: Gloves, eye protection; add acid to water (never water to acid); keep acid and chlorine stored well apart.

The Pool Life “kill-and-clear” sequence

1) Restore circulation (10–15 min)

• Scoop leaves; empty skimmer/pump baskets.
• Water level 2/3 up skimmer mouth; pump fully primed (no air in lid).
• Aim returns to swirl the surface and move water along walls/steps.

Why: Chemicals only work if water moves into every corner.

2) Set pH to ~7.2

• Test and lower with small acid doses; circulate 30–60 minutes and retest.

Why: Chlorine is far more effective at the lower end of the safe pH range.

4) Brush like you mean it

• Brush walls, steps, lights, behind ladders, corners, and the waterline.
• Expect green to shift toward grey/teal—that’s the biofilm breaking.

5) Filter 24/7 & babysit FC (Day 1–2)

• Run the pump continuously until the water is blue/grey.
• Backwash sand/DE at +8–10 psi over clean pressure; hose cartridges when pressure rises or flow drops.
• Test FC every 4–8 hours on Day 1; top up to your shock level whenever it falls.

Goal: Hold killing FC until the algae is dead, not just faded.

6) Clear the cloud (pick one)

• Clarifier (easy mode): Helps clump fine particles for the filter. Keep filtering; clean the filter as it loads.
• Floc (fast mode): For heavy muck or a deadline. Dose, turn the pump off overnight, let it settle, then vacuum to waste slowly the next day. Top up water and rebalance.

Don’t run floc through cartridges/DE, and never use clarifier + floc together.

7) Rebalance once it’s blue but hazy

Correct in this order: TA → pH → CH → CYA → FC (return to normal range).

Salt pools: Verify salinity is within specification and descale the cell if necessary.

Special algae types

Mustard/Yellow algae

• Loves shady walls/behind ladders and can survive “normal” shocks.
• After clearing, hold the FC at the high end for 24–48 hours; brush daily. Expose toys, poles, robots, and swimsuits to chlorinated water or full sun.

Black spot (concrete pools)

• Rooted colonies; very stubborn.
• Use a stainless brush, targeted chlorine applications, and sustained high FC over weeks. Persistence wins.

Should I use algaecide?

• During recovery, chlorine at shock level is the primary killer.
• Quats/polyquats can help after clearing as a preventive measure in challenging seasons.
• Be cautious with copper algaecides (staining risk, especially on light surfaces). If you use metals, pair with a sequestrant and manage pH closely.

Common mistakes (and quick fixes)

• Relying on the salt cell to shock: Use liquid chlorine for the big lift.
• Big, single chemical dumps: Dose in stages; circulate and retest—especially for pH and CYA.
• Skipping brushing: It’s the cheapest, most effective “algaecide.”
• Too little filtration: Run longer on low RPM; clean the filter as soon as pressure rises.
• CYA creep from tablets: High CYA slows chlorine. Use tablets sparingly; favour liquid chlorine/SWG for maintenance.
• Shocking with pH too high: Fix pH first, then shock.

A realistic timeline

• Day 0: Green → teal after shock & brush.
• Day 1: Cloudy blue/grey; maintain shock level; filter working hard.
• Day 2–3: Significant clearing; fine silt on floor.
• Day 3–5: “Polish” phase; water goes from clear to sparkling.

(Severe blooms, undersized/dirty filters, or very high CYA can extend this.)

Keep algae from coming back.

• Match FC to CYA: Keep stabiliser in range and FC steady for that CYA.
• Run time: Increase hours/output in hot, sunny periods.
• Brush weekly; scoop leaves early.
• Phosphates: If heavy leaf loads or recurring blooms persist, a phosphate remover can help reduce nutrient load.
• Log tests/doses: Patterns show before problems do.

When to call Pool Life

If your pool stays dull 48–72 hours after this plan—or keeps greening—we’ll run a full diagnostic: water test (FC/CC, pH, TA, CH, CYA, salt), circulation audit, filter/media inspection, and a simple prevention program tailored to your pool.