Pool algaecide works by targeting algae at the cellular level — either breaking down cell walls, disrupting outer membranes, or inhibiting algae growth through metal ions. There are three main types used in domestic pools: quaternary ammonium compounds (quats), polyquat (polymer algaecide), and copper-based formulas. Each suits different situations: quats are the most affordable entry point, polyquat is the most versatile non-staining option, and copper-based algaecide is the strongest treatment for severe or recurring infestations. This guide covers how each type works, UK pricing, dosage instructions, and when algaecide should and shouldn’t be added to a pool.
- Three types of pool algaecide: quaternary ammonium (quat, 50% concentration), polyquat/Poly-60 (60% concentration, non-foaming), and copper-based (~11.8% copper, up to 90 days protection).
- Polyquat is 2× faster than standard quat algaecides and does not foam, stain, or affect pH — the recommended choice for most UK domestic pool owners.
- Never add algaecide and shock chlorine simultaneously — add algaecide after the chlorine level has dropped back to normal (typically 24 hours after shocking).
- UK polyquat algaecide pricing: 1L £10.99, 2.5L £19.99, 5L £30.99. Standard treatment dose for established algae: 1L per 10,000 gallons.
Types of Pool Algaecide: Quat, Polyquat and Copper-Based
All three algaecide types work to eliminate or suppress algae growth, but they differ in speed, concentration, the types of algae they address most effectively, and the side effects they carry. Choosing the wrong type for your situation can mean either an underpowered treatment or unnecessary staining and foaming.
Quaternary Ammonium (Quat) Algaecide
Quaternary ammonium compounds — commonly called quats — are biocides that work by breaking down algae cell walls, disrupting their internal structure and causing cell death. Standard quat algaecides are typically sold at 50% concentration. They are the most commonly available and cost-effective algaecide on the market, and they work against all three of the most common pool algae types: green/blue-green, yellow (mustard) and black algae.
The main practical limitation of quat algaecides is foaming: at higher doses — or if the pool is agitated before the product has dispersed — quat products can produce visible foam on the water surface. This dissipates naturally but can be alarming on first use. Quats are compatible with both summer and winter pool use, making them a cost-effective maintenance option throughout the year. For preventative weekly dosing in a well-maintained pool, a standard quat algaecide is the most economical choice.
Polyquat (Poly-60) Algaecide
Polyquat algaecides — also labelled Poly-60 for their 60% polymer concentration — work by attaching directly to algae cells and degrading their outer protective membrane, preventing further growth and killing existing algae. They are approximately twice as fast-acting as standard quat algaecides, and are formulated to be non-foaming, pH-neutral and non-staining — the three main drawbacks of cheaper quat products are absent with polyquat.
Polyquat is a non-metallic formula, which means it does not carry the staining risk associated with copper-based products. In the UK, polyquat algaecide from Swimming Pool Chemicals (containing Polyquaternary Ammonium Chloride) is available in three sizes: 1 litre at £10.99, 2.5 litres at £19.99, and 5 litres at £30.99. For most UK domestic pool owners, polyquat is the recommended choice: it handles green, yellow and black algae effectively without staining, foaming or altering water chemistry.
Copper-Based Algaecide
Copper-based algaecides use the algaestatic properties of copper ions — which are toxic to algae — to kill and suppress growth. Products in this category typically contain around 11.8% copper (as in Robelle 3 Month Algaecide), and the higher the copper concentration the greater the kill effectiveness. A significant advantage of copper-based formulas is duration: a single treatment can provide up to 90 days of protection, compared to the weekly dosing required with quats and polyquat.
The main risk with copper-based algaecide is staining. If the product is overdosed or the water chemistry is not properly balanced before application, copper residues can cause blue-green staining on pool walls, liners and equipment. This is difficult to reverse once it occurs. Copper-based algaecide is most appropriate for severe or recurrent algae infestations — particularly black algae, which requires a stronger treatment than quats can typically provide — but should be applied carefully following the manufacturer’s dosage instructions. For pools with fibreglass or coloured liners, polyquat is generally the safer default.
How to Use Algaecide in a Swimming Pool
The effectiveness of any algaecide depends heavily on timing and water conditions. Adding algaecide to an unbalanced pool or at the wrong stage of a treatment sequence significantly reduces its impact — and in the case of quat and copper products, can create additional problems.
When to Add Algaecide: After Shocking, Not Simultaneously
Algaecide and chlorine shock must never be added to a pool at the same time. When chlorine is at a shock level — typically 5–10 ppm for superchlorination — it breaks down algaecide molecules before they can reach and act on algae cells, wasting the product entirely. The correct sequence is to shock the pool first, then wait at least 24 hours for chlorine to return to normal operating levels (1–3 ppm) before adding algaecide.
Water chemistry should be balanced before application: pH must be in the range of 7.2–7.6 and alkalinity stable. Adding algaecide to water outside this pH range reduces its effectiveness. The pool pump should be running when algaecide is added, and should continue running for at least a couple of hours after application to distribute the product throughout the pool volume.
Dosage and Application
Dosage varies by algaecide type and the severity of the algae problem. For polyquat algaecide used as a treatment against established algae, the standard dose is 1 litre per 10,000 gallons of pool water. For weekly preventative maintenance dosing, the required amount drops significantly to 100ml per 10,000 gallons. At the start of the pool season — before algae has had a chance to establish — a full 1 litre per 10,000 gallons is recommended.
The correct application method is to dilute the required amount of algaecide in warm water in a plastic bucket first, then add the diluted solution slowly via a skimmer or distribute it evenly around the pool perimeter while walking the pool edge. Direct pouring from the bottle into a single location concentrates the product and increases the risk of staining or foam. After application, leave the pump running and avoid swimming for the recommended interval stated on the product label — typically 15–30 minutes for polyquat, longer for copper-based products.
Maintenance Dosing and Prevention
Algaecide is most effective when used as a preventative tool rather than a reactive treatment. A weekly or bi-weekly maintenance dose during the swimming season keeps algae spores from establishing and prevents the full algae blooms that require larger shock treatments to address. In pools with regularly fluctuating chlorine levels — common in outdoor UK pools that see variable sunlight and bather loads — the protective buffer provided by regular algaecide dosing is particularly valuable.
For pool owners who prefer longer intervals, the copper-free All Year Long Algaecide (available from UK Pool Store) treats up to 10,000 gallons per 1L application and prevents most types of algae for up to 3 months during the summer season. Copper-based products at 11.8% concentration similarly offer up to 90 days of protection per dose. For context on broader pool water management including chlorine and pH maintenance, see our guide to types of swimming pools, which covers how pool construction affects chemical maintenance requirements.
| Type | Concentration | Speed | Foaming | Staining Risk | Duration |
|---|---|---|---|---|---|
| Quat | 50% | Standard | Yes (high doses) | None | Weekly dose |
| Polyquat | 60% | 2× faster | No | None | Weekly dose |
| Copper-based | ~11.8% Cu | Fast | No | Yes (if overdosed) | Up to 90 days |
Frequently Asked Questions
What is algaecide for pools?
Pool algaecide is a chemical treatment used to kill existing algae or prevent algae growth in swimming pools. The three main types are quaternary ammonium (quat) compounds, polyquat (Poly-60) algaecides, and copper-based algaecides. Each type works by disrupting algae cell membranes or using metal ion toxicity to inhibit growth. Algaecide is used alongside chlorine and regular shock treatments as part of a complete pool maintenance routine.
When should I add algaecide to my pool?
Add algaecide after shocking — wait at least 24 hours for chlorine levels to return to normal (1–3 ppm) before adding algaecide. Never add both simultaneously, as high chlorine levels break down algaecide before it can act. Balance pH to 7.2–7.6 first, run the pump, and add algaecide via dilution in a bucket distributed evenly around the pool.
How much algaecide do I add to my pool?
For polyquat algaecide: 1 litre per 10,000 gallons to treat established algae, or 100ml per 10,000 gallons for weekly prevention. For the start of the swimming season, use the full treatment dose (1L per 10,000 gallons). Copper-based algaecides vary by brand — always follow the specific product’s dosage instructions to avoid staining.
Can I use algaecide and chlorine at the same time?
No. Adding algaecide and chlorine shock simultaneously means the high chlorine level destroys the algaecide before it can work on the algae. Always shock first, wait 24 hours for chlorine to drop to 1–3 ppm, then add algaecide. Routine maintenance chlorine (not shock levels) and low-dose algaecide can be used on the same day when chlorine is within normal range.
What is the best algaecide for a UK swimming pool?
Polyquat (Poly-60) algaecide is the most versatile option for UK domestic pools: non-foaming, non-staining, pH-neutral and twice as fast as standard quat algaecides. Swimming Pool Chemicals supplies UK polyquat algaecide from £10.99 per litre. For severe infestations — particularly black algae — a copper-based algaecide may be more effective, but requires careful dosing to avoid staining.
Does algaecide affect pool pH?
Polyquat algaecides are pH-neutral and do not alter water chemistry. Standard quat algaecides also have minimal impact on pH. Copper-based algaecides can slightly lower pH over time. In all cases, pH should be balanced to 7.2–7.6 before adding algaecide rather than relying on algaecide to correct imbalances.
