What's wrong
with your pool?
Select your problem. A few quick questions, then an exact fix plan.
How green is the water?
This helps us determine how severe the algae problem is and how aggressive the treatment needs to be.
Do you know your pool volume?
We need this to calculate exact chemical amounts.
Don't know? Calculate it here →
Your Fix Plan: Green Pool Water
For a 15,000 gallon pool with medium green water
Brush the pool
NowBrush all walls, floor, steps, and behind ladders to dislodge algae from surfaces. This exposes algae to the chlorine you'll add next.
Triple shock
At sunsetAdd 3x the normal shock dose to kill the algae bloom. Do this at sunset for maximum effectiveness.
Liquid Chlorine (12.5%)
Recommended
1.5 gallons
Cal-Hypo Shock (65%)
Alternative
2 lbs
Run pump 24 hours
Keep the pump running continuously until the water clears. Backwash or clean the filter every 8-12 hours — it'll be catching a lot of dead algae.
Test again
Next morningTest FC. If it dropped below 5 ppm overnight, the algae is consuming chlorine faster than expected — add another dose. If FC held, the algae is dying.
Ready to swim
24-72 hoursWhen the water is clear and FC is between 1-3 ppm, you're safe to swim. Run the Water Balance tool to make sure everything else is in range too.
Safety: Never mix chlorine with acid. Wear gloves and eye protection. Don't swim until FC is below 3 ppm. Follow product label instructions.
What changed most recently?
Cloudy water has a few common causes. Pick the closest match — the plan covers all of them.
Your Fix Plan: Cloudy Water
Most cloudiness is filtration plus minor imbalance. Work top to bottom.
Test and balance the basics
NowTest FC, pH, TA and calcium hardness. Cloudiness often comes from pH or calcium drifting high (water starts to scale) or FC sitting too low (early algae looks like haze before it turns green). Bring pH to 7.2-7.6 first.
Run the pump 24/7 and clean the filter
Same dayThe filter is what physically removes the haze. Run the pump continuously and clean or backwash the filter once it loses pressure. A dirty or undersized filter is the single most common cause of cloudy water that won't clear.
Add a clarifier or flocculant
A clarifier clumps fine particles so the filter can catch them — gentle, takes a day or two. A flocculant drops everything to the floor for you to vacuum to waste — faster but more work and water loss. Use clarifier first unless the pool is badly clouded.
Best for slightly hazy water. Add, run filter, wait 24-48h.
For heavy cloudiness. Drops particles to the floor — vacuum to WASTE, not through the filter.
Confirm chlorine is high enough
Same dayLow free chlorine lets a haze build before visible algae. Make sure FC matches your CYA level. Use the shock calculator for the exact amount for your pool.
Shock Calculator
Get my exact shock dose
Re-test and wait
24-72 hoursWith the pump running and the filter clean, water clears within 1-3 days. If it's still cloudy after that with FC in range, the filter is the bottleneck — deep-clean or check filter media.
Safety: Don't let anyone swim while you can't clearly see the main drain — a hidden swimmer is a drowning risk. Never mix chemicals; add one at a time with the pump running.
When did the foam show up?
Foam is almost always one of three things. Pick when it started.
Your Fix Plan: Foamy Water
Foam means something in the water lowers surface tension — usually algaecide, low calcium, or high TDS.
Stop adding algaecide
NowCheap quat / poly-quat algaecides are the #1 cause of pool foam. If foam started after you dosed one, that's it — don't add more. The foam fades on its own as the algaecide breaks down over a few days.
Check calcium hardness
Soft water (calcium hardness below ~150 ppm) foams easily because there's nothing to hold surface tension. Raise it toward 200-400 ppm with calcium chloride if it reads low.
Calcium Hardness Calculator
Get my calcium dose
Add a defoamer for a quick fix
Same dayA pool defoamer knocks the foam down within minutes. It treats the symptom, not the cause — fine while you sort out the calcium or wait out the algaecide.
Partial drain if water is old
If TDS is highYears-old water builds up dissolved solids (TDS) that won't filter out and keep the water foaming. Drain 25-50% and refill with fresh water, then re-balance.
Drain a quarter to half. Full drains risk a pool 'floating' out of the ground — don't fully empty an in-ground pool without advice.
Re-test and re-balance
24 hoursFoam should be gone within a day. Re-check pH, FC and calcium after any drain so the water stays balanced.
Safety: Foam itself isn't harmful, but don't keep dumping algaecide to 'fix' it — that makes it worse. Add calcium and water-balance chemicals separately, never together.
Can you test combined chlorine?
That strong chlorine smell almost always means too LITTLE active chlorine, not too much. We'll confirm it.
Your Fix Plan: Chlorine Smell
The smell is chloramines — spent chlorine. The fix is more chlorine, not less.
Understand what you're smelling
NowA clean, well-chlorinated pool has almost no smell. The strong 'chlorine' odour is chloramines — chlorine that's already bonded with sweat, oils and urine and is used up. It signals you need to shock, not back off.
Measure combined chlorine
Combined chlorine (CC) = Total chlorine − Free chlorine. Anything above 0.5 ppm causes the smell and eye irritation. If you can only read FC, assume CC is high if the smell is strong.
Shock to breakpoint
At duskTo break the chloramine bond you have to raise free chlorine to roughly 10× the combined chlorine reading at once — 'breakpoint' chlorination. Do it at dusk so sunlight doesn't burn off the chlorine. Use the shock calculator for your pool's exact dose.
Shock Calculator
Get my breakpoint dose
Run the pump and re-test
8+ hoursKeep the pump running overnight to circulate. In the morning re-test: combined chlorine should be back near 0 and the smell gone. If CC is still up, shock again.
Prevent the next time
Keep FC in range for your CYA, ask swimmers to rinse off before getting in, and shock weekly during heavy use. Chloramines build up faster the more the pool is used.
Safety: Never mix chlorine with acid or with other shock types. Add shock to water (not water to shock), with the pump running. Don't swim until FC is back below 3 ppm.
What colour are the patches?
Different algae need different treatment. The colour tells us which one you've got.
Your Fix Plan: Algae on Walls
Every type needs brushing plus chlorine — the colour just changes how aggressive you go.
Brush every affected surface
NowAlgae hides under a protective layer that chlorine can't reach until you break it open. Brush walls, floor, steps and behind ladders hard. Use a stiff nylon brush for green and mustard; black algae needs a steel brush or pumice on plaster.
Roots into plaster and grout. Brush hard enough to expose the spots — they will keep coming back otherwise.
Balance pH, then shock
At duskChlorine works best at pH 7.2-7.4 — bring pH down first if it's high. Then shock at dusk. Green needs a normal-to-triple shock; mustard and black need a higher, sustained level held for longer.
Triple shock once, hold FC high until water clears.
Shock higher and brush daily — it resists chlorine and re-appears in shade.
Shock to the high end and hold for several days; scrub each spot directly.
Shock Calculator
Get my shock dose
Add the right algaecide if it resists
If chlorine alone isn't winning, a polyquat (60%) algaecide helps with green and is foam-free. Mustard and black often need a specialised copper or ammonium algaecide — follow the label dose.
Brush daily and run the filter
3-5 daysKeep the pump running 24/7 and brush once a day until every trace is gone. Backwash or clean the filter often — it's catching dead algae.
Vacuum, re-test, and balance
When clearVacuum up dead algae (to waste if heavy), then re-balance the water. Black algae especially — if you stop early it regrows from the roots.
Water Balance tool
Re-balance the water
Safety: Never mix chlorine with acid or algaecide. Add chemicals separately with the pump running. Keep brushes and pumice off vinyl liners — they tear.
Do you have a pH test?
Burning eyes is usually pH out of range — not 'too much chlorine' like most people think.
Your Fix Plan: Burning Eyes & Skin
Comfortable water sits at pH 7.4-7.6 — the same as your tears. Off-range pH and chloramines are what sting.
It's the pH, not the chlorine
NowThe myth is 'too much chlorine'. In reality, eyes sting when pH drifts out of the 7.2-7.8 comfort band, or when chloramines (spent chlorine) build up. Properly balanced chlorinated water doesn't burn.
Test pH and combined chlorine
Check pH first — aim for 7.4-7.6. Then check combined chlorine; above 0.5 ppm it irritates eyes and skin and smells. Both can be at fault at once.
Bring pH back into range
Same dayHigh pH → add muriatic acid or dry acid. Low pH → add soda ash. Re-test after a few hours of circulation. Most eye irritation clears the moment pH is back in band.
pH Calculator
Get my pH adjustment
Shock if combined chlorine is high
At duskIf CC is above 0.5 ppm, shock to breakpoint to clear the chloramines that irritate eyes and skin. Use the shock calculator for the exact amount.
Shock Calculator
Get my shock dose
Re-test before anyone swims
After circulatingConfirm pH 7.4-7.6 and combined chlorine near 0. Ask swimmers to shower first — body oils and sweat are what create chloramines in the first place.
Safety: Always add acid to water, never water to acid, with the pump running. Never mix acid and chlorine. Wear gloves and eye protection when handling either.