Pool algaecide treatment: curative or preventive?

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Pool algaecide: do you need a curative or a preventive treatment?

Water turning green, slippery walls: that means algae. Here is how to choose the right algaecide for the condition of your water — and above all how not to pick the wrong product.

Green or cloudy water
→ CURATIVE treatment (shock)
The algae are already there. You need a powerful product that destroys them quickly. The preventive product won't manage it.
Clear water
→ PREVENTIVE treatment (maintenance)
The water looks great: we help it stay that way. A regular dose stops algae from settling in, all season long.

Why is my water turning green?

Algae are micro-organisms that are always present in the air and in water. They multiply suddenly as soon as three conditions come together: heat, light and insufficient disinfection (chlorine too low, filtration too short, pH thrown off after a storm or heavy use).

Within 24 to 48 hours, the water turns green, the walls become slippery and the floor clouds over. It is not dangerous in itself, but it is a sign that the disinfectant is no longer doing its job — and green water can quickly become unfit for swimming.

Green water: why use a curative treatment and above all NOT a preventive one?

The mix-up to avoid

Many people, seeing green water, pour in their usual preventive algaecide… and are disappointed: the water stays green. That is normal. The two products do not have the same role.

The preventive product is designed to stop algae from appearing in water that is already clean: it is too weakly concentrated to overcome an established invasion. The curative (shock) product is far more powerful: it is designed to destroy algae that are already present.

A simple image to remember: the preventive product is the seat belt — useful before the accident. The curative product is the emergency services — the ones you call when the accident has happened. Using a preventive on water that is already green is like buckling your seat belt once the car is in the ditch: too late, it is no longer the right tool.

So: green water = curative shock treatment. The preventive product takes over afterwards, once the water is clear again.

1The curative treatment: recovering green water

The emergency treatment, when algae are visible: green or milky water, slippery walls, stains on the liner.

Blackal Shock Shock Algaecide — 1 L
22,99 €
HTH
 Curative · Shock

Blackal Shock Shock Algaecide — 1 L

Why this product? it destroys all types of algae, even the most resistant ones (“mustard”, “black” and “pink” algae) thanks to its copper-based formula — treated to avoid staining the lining or swimmers' hair. It is the product that turns green water clear again.

Advantages
✔ Fast, powerful action on water that is already green
✔ Effective on resistant algae (mustard, black…)
✔ Anti-staining formula (liner & hair protected)
✔ Pool and spa
Drawbacks
✘ One-off treatment, not ongoing maintenance
✘ Long filtration needed after application
✘ To be combined with shock chlorine if the water is very green

View product →
How to use it (green water)
  1. Adjust the pH to between 7.0 and 7.4: an algaecide works poorly in water with an unbalanced pH.
  2. Brush the walls and floor to loosen the algae clinging to them.
  3. Do a shock chlorination at the same time to disinfect thoroughly.
  4. Pour in the shock algaecide at the curative dose, in front of the return jets.
  5. Run the filtration continuously for 24 to 48 hours, then vacuum and clean the filter.

2The preventive treatment: keeping the water clear

Once the water is clear (or from the start of the season), you switch to maintenance: a regular dose that keeps algae from coming back, with no need for another shock treatment.

Super Kleral — 3 L
38,99 €
HTH
 Preventive · Maintenance

Super Kleral — 3 L

Why this product? it is a “multifunction” maintenance product: it stops algae from returning, fights scale and metal deposits, and makes the water crystal clear. Non-foaming, it is simply added to the regular pool water. Ideal for lasting the whole season without any nasty surprises.

Advantages
✔ Durably prevents algae from coming back
✔ 2-in-1: algaecide + anti-scale
✔ Clearer water, non-foaming
✔ Large 3 L size, economical over the season
Drawbacks
✘ Cannot recover water that is already green on its own
✘ Requires a regular dose (don't forget it)
✘ Higher initial outlay (large size)

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How to use it (maintenance)
  1. On clear water with a balanced pH (7.0 – 7.4).
  2. Add the maintenance dose every week, in front of the return jets, with the filtration running.
  3. After intense heat, a storm or lots of swimmers, repeat the dose.
  4. Keep a proper disinfectant (chlorine) level and adequate filtration: that is the real foundation of prevention.

Curative or preventive: the comparison

 Curative — Blackal ShockPreventive — Super Kleral
When to use it Green / cloudy water, visible algae Clear water, regular maintenance
Role Destroy established algae Prevent algae from appearing
Strength High (shock treatment) Maintenance dosage
Frequency Occasional, when there is a problem Every week, all season
Extra benefit Effective on resistant algae Anti-scale + crystal-clear water
Price 22,99 € (1 L) 38,99 € (3 L)

The right approach in a nutshell

Is my water green? → Curative shock treatment (Blackal Shock): we get the water clear again.
Is my water clear? → Preventive treatment (Super Kleral): we keep it looking great, effortlessly.

And in every case, the best prevention remains well-balanced water: a pH between 7.0 and 7.4, a disinfectant at the right level and sufficient filtration (roughly, the water temperature ÷ 2, in hours per day). An algaecide is a supplement, not a replacement for chlorine.

Choose your algaecide treatment

Water to recover or water to protect? Our two HTH treatments cover both situations.

Shock Algaecide (curative) Super Kleral (preventive)
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