What should I do when pool water suddenly turns green?

Green water almost always means algae. First adjust the pH to 7.0–7.4 – outside this range, chlorine works significantly less effectively. Then place 5-in-1 chlorine tablets in the skimmer and add a liquid algaecide for severe infestations. Increase filter running time to at least 12 hours daily. A visible improvement should be apparent after 24–48 hours.

Does algaecide help against cloudy, milky water?

No – algaecides combat algae, but not the fine suspended particles that cause milky water. If chlorine levels are correct but the water remains cloudy, a flocculant clarifier like Cristal Klareffekt is the right choice. It clumps invisible particles together so the filter can remove them.

Do I have to completely drain the pool if the water is heavily green?

In most cases, no. Even heavily green water can be treated with chlorine and algaecide as long as the filter pump is running and products are correctly dosed. Only when the pool is completely green-sludgy and the bottom is no longer visible might a full water change be faster than chemical treatment.

How long does it take for pool water to clear after treatment?

For algae problems, typically 24–72 hours depending on severity and filter running time. For suspended-particle turbidity with a flocculant, often visibly better within a few hours. The process is faster when the filter runs continuously and is backwashed regularly.

Are standard chlorine tablets suitable for children's pools?

Standard pool chlorine tabs are generally overdosed for paddling pools and very small children's pools. A chlorine-free product like Söll AquaDes is much better suited for these applications. For larger above-ground pools where children swim, chlorine tabs can be used at the correct dosage – checking the recommended minimum pool size on each product is essential.

Use case

Green or Cloudy Pool Water: Step-by-Step Back to Crystal Clear

Whether algae or stubborn suspended particles – cloudy pool water needs a different solution for each cause. This guide explains how to make the right diagnosis and which product genuinely delivers results.

Reviewed on June 9, 2026Curated by Sascha Camin

As an Amazon Associate I earn from qualifying purchases.

You lift the pool cover after a long weekend or the first spring day – and instead of crystal-clear water, you're greeted by a greenish or milky-cloudy pool. One of the most common frustration moments of the swimming season. Yet the situation is almost always fixable – as long as you reach for the right product.

The crucial first step is the diagnosis: Green water is almost exclusively caused by algae that multiply rapidly when chlorine levels drop or temperatures rise. Cloudy, milky water often has an entirely different root cause – precipitated lime particles, fine suspended matter, or an overloaded filter that can no longer capture the smallest particles. Confusing these two scenarios and using the wrong product wastes time and risks prolonging the problem.

This guide organises six products by use case – from simple ongoing chlorination to specialised algaecide to chlorine-free children's pool treatment – and explains which combination gets the pool back to clear the fastest for each problem.

Step 2 · Decision

Which one fits you?

If Green water, medium to large pool, simple application desired
Our pick
BAYZID Chlorine Multi-Tabs 5-in-1Researched
BAYZID Chlor Multitabs 5 in 1 combine all five care steps in one tablet and are the most widely reviewed choice with thousands of ratings. Drop in skimmer – done. The high review count provides confidence for first-time buyers.
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If Green deposits on walls or recurring algae problems
Our pick
Steinbach Liquid Algaecide 5 LResearched
Steinbach Algezid flüssig is highly concentrated, foam-free, and specifically developed against algae growth. Flexible dosing: light prevention at 20–40 ml, severe infestations up to 600 ml per 10 m³. Also suitable for pre-treating pool walls before filling.
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If Cloudy, milky water despite correct chlorine levels
Our pick
Cristal Klareffekt Pool ClarifierResearched
When chlorine is correct but water stays cloudy, suspended particles are the problem. Cristal Klareffekt flocculates the finest particles so the filter can capture them – works with sand and cartridge filters.
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If Smaller pool under 25 m³ needing precise chlorine dosing
Our pick
BlueViking 5-in-1 Pool Chlorine TabsResearched
BlueViking recommends 1 tablet per 2 m³ – a specific dosing guideline that prevents over-dosing in smaller pools. BAuA-registered (N-106206), Made in Europe, with German-language manufacturer support.
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If Children's pool, paddling pool, or above-ground pool with frequent water changes
Our pick
Söll AquaDes Pool Disinfectant 2.5 lResearched
Söll AquaDes disinfects without chlorine against bacteria and germs – the right solution for paddling pools and children's pools where high chlorine concentrations are undesirable and water is regularly renewed.
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Section 1

How we selected

Pool care products are available in great numbers, but with green or cloudy water, one thing matters above all: the mechanism of action must match the cause. We therefore did not search for the most promising brand name, but for products with a clearly defined use case, a substantial number of independent user reviews, and verifiable approval under EU biocide standards. The BAuA registration number – explicitly stated for BlueViking, MEINPOOL24.DE, and Steinbach – is a more reliable quality signal than marketing promises. This selection covers products for three different problem scenarios: algae growth (green water), suspended-particle turbidity (milky water without an algae problem), and the special case of children's pools.

Section 2

Fighting green water: the key use cases

Season opening after the winter break: Opening the pool in spring and finding green water is the classic algae problem. Chlorine multitabs (BAYZID, MEINPOOL24.DE, or BlueViking) help as basic disinfection, supplemented by Steinbach Algezid for severe infestations. Filter running time should be increased to at least 12 hours daily during this phase.

Sudden tipping during heatwaves: High temperatures cause algae to explode – pools can turn green within 24–48 hours. The 5-in-1 chlorine tabs work slowly and continuously, which sometimes needs to be supplemented by a short-term shock chlorination for acute infestations. Steinbach Algezid provides the necessary flexibility for these situations thanks to its variable dosage.

Regular maintenance as prevention: Anyone who adds a chlorine multitab every one to two weeks and occasionally doses algaecide preventively rarely experiences green water at all. BAYZID and MEINPOOL24.DE are well suited to this as uncomplicated ongoing companions throughout the season.

Section 3

Cloudy water and the underestimated filter factor

Cloudy water that is not an algae problem is often mishandled by pool owners – more chlorine, more algaecide, but the water stays milky. The real bottleneck is in the filter: particles finer than approximately 20 micrometres are not captured by sand filters. Cristal Klareffekt works as a chemical filter enhancer: its active ingredients cause these invisible particles to clump together (flocculation) until they are large enough for the filter. The result is visible within a few hours – provided the filter is running and backwashed regularly after treatment. Cristal is compatible with sand and cartridge filters according to the manufacturer, making it the universal solution for stubborn residual turbidity that does not respond to chlorine.

Section 4

Which product for which situation

Green water, medium to large pool: BAYZID or MEINPOOL24.DE Chlor Multitabs 5 in 1 as baseline care; add Steinbach Algezid for deposits on pool walls.

Green water, smaller pool under 25 m³: BlueViking with its clear 1-tablet-per-2-m³ dosing gives more control over chlorine quantity and avoids over-dosing.

Cloudy but not green water: Cristal Klareffekt – not algaecide, not additional chlorine, but targeted flocculation of invisible particles.

Children's pool or paddling pool: Söll AquaDes as a chlorine-free alternative for situations where chlorine is not the first choice and water is changed frequently.

Preventive ongoing maintenance: Chlorine multitabs from BAYZID or MEINPOOL24.DE are sufficient for most pools when values are checked regularly.

Verdict

For green pool water, chlorine multitabs – BAYZID or MEINPOOL24.DE for medium to large pools, BlueViking for smaller ones – combined with Steinbach algaecide are the fastest route back to clear water. Cloudy, milky water without an algae problem calls for Cristal Klareffekt, not more chlorine. Children's pools and paddling pools benefit from chlorine-free Söll AquaDes. Getting the diagnosis right before the first product choice saves time, frustration, and an unnecessary second attempt.