Clear pool water does not happen by accident. Most clarity problems trace back to one of three root causes: a chemistry imbalance, poor or insufficient filtration, or too high an organic load. Knowing which cause is driving your problem is the difference between a fix that works and one that wastes time and chemicals.
This guide covers the 7 most effective methods to clear cloudy, green or foamy pool water, explains what is causing each type of problem, and includes specific guidance for the two most common scenarios: green water from algae and white or grey haze from chemistry issues.
Why pool water turns cloudy
Cloudy water is always a symptom of something else going wrong. The appearance of the cloudiness is the first clue to the underlying cause.
| Cause | Appearance | Quick solution |
|---|---|---|
| Low chlorine | Green tint, flat smell, slightly hazy | Add chlorine or shock treat |
| High pH | White milky haze | Add pH minus, retest after 4 hours |
| Poor filtration | Persistent haze despite correct chemistry | Backwash filter, increase run time |
| High combined chlorine (chloramines) | Haze plus eye and skin irritation | Shock treatment to break chloramine lock |
| Algae bloom | Green, yellow or black patches or tint | Shock plus algicide, brush walls |
| Body oils and sunscreen | Slightly foamy or grey, greasy sheen | Enzyme clarifier, more filter run time |
The most common combination is pH drifting above 7.6 together with low free chlorine. When pH is too high, chlorine loses most of its effectiveness - at pH 8.0 only around 20 percent of your chlorine is in the active form. This creates the conditions for bacteria and algae to establish quickly.
Poor filtration is the second most overlooked cause. A filter that is dirty, clogged or only running 4 to 5 hours per day cannot remove the fine suspended particles that cause haze, even if the chemistry is balanced.
7 methods to clear pool water
Work through these methods in order. Steps 1 and 2 must come before anything else - adding flocculant to a chemically imbalanced pool achieves nothing.
1. Test and balance the water
Always start here. There is no point adding products if you do not know what the water needs. Measure pH, free chlorine and total alkalinity before doing anything else.
Target values:
- pH: 7.2 to 7.6
- Free chlorine: 1 to 3 mg/l
- Total alkalinity: 80 to 120 mg/l
Use test strips for a quick read, but for accurate results use a liquid drop test kit or a digital tester. If alkalinity is low (below 80 mg/l), the pH will be unstable and difficult to correct - raise alkalinity first with a total alkalinity increaser before adjusting pH.
2. Shock treatment
If chlorine is low, combined chlorine is high, or you are dealing with algae, shock treatment is the second step. Shock means raising the free chlorine level to 10 to 30 mg/l - well above the normal 1 to 3 mg/l range - to destroy chloramines, kill algae spores and oxidise organic matter.
Use granular calcium hypochlorite or a dedicated pool shock product. Pre-dissolve in a bucket of pool water before adding. Shock in the evening or at night so UV does not break down the chlorine before it can work. Run the pump during and after treatment.
Tip
Do not mix different shock or chlorine products together, even if they are both described as pool chlorine. Different chemical forms can react dangerously. Always add each product separately to the pool with the pump running and never into the skimmer at the same time.
3. Run the filter for 8 to 12 hours minimum
During a clarity problem, run the pump continuously or for at least 8 to 12 hours per day. Filtration is the mechanical process that actually removes particles from the water - chemicals alone cannot do this. Even after balancing chemistry, you need sufficient filter run time to see results.
If you normally run your pump for 6 hours per day in summer, increase to 10 to 12 hours during any clarity problem.
4. Backwash or clean the filter
A dirty filter is one of the most common reasons pool water stays cloudy despite correct chemistry. Sand filters should be backwashed regularly - typically when the pressure gauge reads 0.5 bar above its clean baseline, or at least every 2 weeks during heavy use.
To backwash: set the multiport valve to backwash, run for 2 to 3 minutes until the water in the sight glass runs clear, then set to rinse for 30 seconds, then return to filter. After a severe algae or cloudiness event, add a filter cleaner product to break down oils and organic matter trapped in the sand.
Tip
Check your filter pressure gauge when the filter is clean and note the reading. Any time the pressure is 0.5 bar or more above that baseline, it is time to backwash. A filter working against high resistance is pushing water around the sand rather than through it.
5. Use flocculant to collect suspended particles
When fine particles are too small for the filter to catch, flocculant binds them together into larger clumps that sink to the floor. You then vacuum them out manually using the waste setting on your multiport valve - this bypasses the filter so the sediment is flushed to drain rather than back into the pool.
Liquid flocculant is easier to use than granular. Pre-dilute in a bucket, add to the pool with the pump running, run the pump for 1 hour to circulate the product, then switch the pump completely off for 24 hours. The flocs settle to the floor as a visible layer of sediment. Vacuum slowly to waste, then backwash the filter.
Tip
Never use flocculant with a cartridge filter. The flocs will clog the cartridge and you will need to replace it immediately. Flocculant is only compatible with sand filters operating on the filter setting during circulation.
6. Check and clean the skimmer and pump baskets
A clogged skimmer basket or pump basket restricts water flow through the entire system, reducing filtration effectiveness. This is a 2-minute check that is often overlooked. Empty both baskets, rinse them out, and check the pump impeller for debris if flow seems low even with clean baskets.
7. Brush the walls and floor before shocking
Algae and biofilm cling to pool surfaces. If you shock the water without first brushing the walls and floor, the biofilm acts as a barrier and the chlorine cannot reach the algae cells effectively. Brush all surfaces thoroughly - walls, floor, steps and around fittings - the day before or just before shocking. This loosens the biofilm and exposes the algae to the chlorine.
Green water: specific steps for algae
Green water is caused by algae growth and requires a more aggressive approach than basic chemistry correction.
- Test and adjust pH to 7.2 to 7.4 (the lower end, where chlorine is most effective)
- Brush all surfaces thoroughly
- Add a high-dose shock treatment - follow product guidance for algae kill dosing, typically 20 to 30 mg/l for your pool volume
- Add algicide after shocking (not at the same time - allow 24 hours between products)
- Run the pump continuously for 24 to 48 hours
- Backwash the filter every 8 hours during heavy algae treatment
- If the water turns grey or blue-grey after shocking, that is dead algae - add flocculant to sink it and vacuum to waste
Severe algae blooms can take 3 to 5 days to fully clear. Repeat shocking may be needed. Do not add flocculant until the active algae are dead - you will know because the colour shifts from green to grey.
White or grey haze: usually a chemistry issue
A white milky haze without any green tint is almost always caused by one of three things: high pH (above 7.8), high calcium hardness or high combined chlorine (chloramines).
Start by testing pH. If it is above 7.6, add pH minus and retest after 4 hours. In many cases, correcting pH alone clears a white haze within 24 to 48 hours of running the filter.
If pH is correct but the haze persists, test total alkalinity and calcium hardness. Very high calcium (above 400 mg/l) can cause calcium precipitation, which appears as a white haze. Partially draining and refilling with fresh water is the most effective solution for high calcium.
Tip
If the water is hazy and swimmers experience eye irritation or a strong chlorine smell, the problem is almost certainly high combined chlorine (chloramines), not low chlorine. Shock treatment is the solution - raising free chlorine to 10 times the combined chlorine reading breaks chloramine compounds. See our guide on pH and chlorine for detail on how to measure combined chlorine.
When cloudiness signals a bigger problem
Most cloudiness resolves with the 7 steps above. Some patterns indicate a structural issue worth investigating further.
Cloudiness returns within days of treatment. If your pool goes from clear back to hazy within 2 to 3 days despite correct chemistry, your filter is almost certainly undersized, worn out or running too few hours. Check filter pressure, increase daily run time and consider whether the sand needs replacing (every 5 to 7 years for a residential pool).
Green but clear water. Clear water with a green or blue-green tint is typically caused by dissolved metals - most commonly copper from tap water or corrosion of metal fittings. Test for metals and treat with a metal sequestrant. Do not shock treat clear green water: adding high chlorine to water with dissolved metals can cause staining on pool surfaces.
Cloudiness immediately after adding chemicals. This sometimes indicates compatibility issues between products or that granular products were not pre-dissolved. Always pre-dissolve granular products in a bucket of pool water and never add two different chemicals to the same spot at the same time.
Product recommendations
Pool Flocculant Liquid 1L
✓ Our pick: Reliable liquid flocculant for fast clearing of cloudy water. Easy to dose, works within 24 hours with a sand filter.
Pool Shock Granules 5kg
✓ Our pick: Fast-dissolving calcium hypochlorite shock. Effective for algae treatment and chloramine removal. Pre-dissolve before adding.