Pool Winter Algaecide - Long Dwell Concentrate

Copper-based winter pool algaecide that prevents algae growth through closed pool months. One dose at close-down keeps water clear under the cover until spring.

• Prevents algae growth through 4-6 months of pool closure.
• Single one-shot dose at winterising.
• Active even at near-freezing water temperatures.
• Compatible with winterising chemicals and pipe antifreeze.
• Cuts spring opening time and chlorine demand.

Sizes and prices

Available in 5L, 10L and 25L bottles.

• 5L: £35.00
• 10L: £66.00
• 25L: £159.00

When you need it

• You are closing the pool for winter.
• Last season ended with mustard or yellow algae problems.
• Pool sits under a cover from October to April.
• You want a low-maintenance winter regime.
• You need an algaecide that survives freezing temperatures.

How to use

1. Wait for water below 12 C before final winter dose.
2. Shock pool to 10 ppm with cal-hypo first; wait 4 hours.
3. Dose 100 ml per 10 m³ of winter algaecide as one-shot.
4. Pre-dilute in 10 L bucket of pool water.
5. Pour evenly around perimeter with circulation on.
6. Run filtration 4 hours, drain pipework, fit winter cover.

Dosing guide

One-shot only at close-down. Do not redose mid-winter. Test for copper at spring opening; if above 0.3 ppm dose sequestrant before re-chlorinating.

• For 20 m³, add 200 ml to reach Winter close-down.
• For 40 m³, add 400 ml to reach Winter close-down.
• For 60 m³, add 600 ml to reach Winter close-down.
• For 100 m³, add 1.0 L to reach Winter close-down.
• For 40 m³, add Up to 600 ml to reach If algae was severe last season.

How it works

Copper sulphate pentahydrate complex with stabilising chelate, giving 4-6% w/w available copper, formulated for cold-water residual activity.

Copper ion disrupts algal photosynthesis by binding to chlorophyll-related enzymes. The chelate keeps copper in solution at low temperatures so it remains active even when chlorine is exhausted.

Chlorine sublimates and decays during winter; copper does not. A single copper dose at close-down outlasts the cover and prevents the green soup that domestic pools find at spring opening.

Frequently asked questions

When do I dose?

At final close-down once water temperature is below 12 C and you have shocked to 10 ppm chlorine.

How much per m³?

10 ml per m³ as a one-shot. For a 40 m³ pool that is 400 ml.

Will it work all winter?

Yes for 4-6 months under cover, longer in cold climates. Re-test at spring opening.

Pack sizes?

1 L and 5 L drums.

Will copper stain my pool?

Only if pH drifts low or copper concentration spikes; staining at correct dose and pH is rare.

Do I need pipe antifreeze too?

Yes. Algaecide protects water; antifreeze protects pipework. Both are needed for winter.

What is the active ingredient?

Chelated copper sulphate pentahydrate at 4-6% w/w available copper.

Why does it work in cold water?

Copper is a metal ion poison to algae and works by direct contact, not enzymatic process; cold does not stop it.

How is copper removed in spring?

Sequestrant binds free copper into a soluble complex that the filter removes; residual is then below 0.3 ppm.

Spring algae?

Shock to 15 ppm; brush; vacuum dead algae to waste; resume polyquat for season prevention.

Stains at opening?

Drop pH to 7.0; brush; dose sequestrant; rebalance.

Winter algaecide vs polyquat?

Winter algaecide is copper-based for cold dormant water; polyquat is for active swim-season prevention. Use one in season, the other for closure.

Winter algaecide vs winteriser?

Algaecide stops algae in the water; winteriser is the broader chemical pack including antifreeze and shock. Use both at close-down.