How to shock your pool UK: If your pool water has gone cloudy, developed a strong “chlorine” smell, or algae has started to appear, it’s probably time to shock the pool.
Shocking is the process of adding a larger-than-usual dose of chlorine (or another oxidising treatment) to quickly destroy bacteria, algae, and chloramines. It’s an essential part of pool maintenance and can restore your water to that fresh, crystal-clear look.
Here’s exactly how to shock your pool correctly in the UK, without wasting chemicals or damaging your pool.
Why UK Pool Owners Need to Shock Their Pools
Even with regular chlorination, contaminants gradually build up in the water. Rainwater, leaves, sunscreen, and increased swimming activity can all reduce chlorine’s effectiveness.
You may need to shock your pool if you notice:
- Cloudy or dull water
- A strong chemical smell (from chloramines)
- Algae growth (green, yellow, or black patches)
- Heavy use by swimmers
- Storms or prolonged rain
In the UK, outdoor pools are more vulnerable during warmer months, while indoor pools can suffer from chloramine build-up if ventilation isn’t perfect.
What You’ll Need
Before you start, make sure you have:
- Your pool water volume – Don’t know? Use our Free Pool Water Volume Calculator
- Pool shock treatment
In the UK, the most common are:- Calcium Hypochlorite granules – strong and cost-effective (needs pre-dissolving)
- Sodium Hypochlorite – liquid chlorine, often used for larger pools
- Non-Chlorine Shock (Potassium Monopersulfate) – good for indoor pools or if you want to swim sooner
- Pool testing kit or test strips
- Protective gloves and safety goggles
- A clean plastic bucket (for mixing, if using granular shock)
- Pool brush (for scrubbing algae spots)
Step-by-Step: How to Shock Your Pool
1. Test the Water
Check your pH first—7.2 to 7.6 is the ideal range for shock treatments to work effectively.
If pH is too high or low, adjust it with pH+ or pH- before you begin.
2. Pick the Right Shock for Your Pool
- Calcium Hypochlorite (granular) – Most popular choice in the UK; ideal for outdoor pools
- Sodium Hypochlorite (liquid) – Often used by commercial pool operators; easy to apply
- Non-Chlorine Shock – Perfect for indoor pools or if you want to avoid raising chlorine levels too much
3. Pre-Mix if Needed
If you’re using granular shock, fill a clean bucket with cold water and slowly add the granules, stirring until fully dissolved.
Important: Always add chemicals to water, never water to chemicals.
4. Add the Shock to the Pool
Pour the solution (or liquid chlorine) evenly around the edges of the pool while the pump is running. For visible algae patches, pour a little extra nearby and brush the area.
5. Keep the Pump Running
Run your circulation system for at least 8–12 hours so the treatment spreads evenly and your filter can remove dead algae and contaminants.
6. Test Before Swimming
The next day, test the chlorine level—it should be between 1–3 ppm before you swim. If it’s still high, wait a little longer.
When to Shock Your Pool in the UK
- Every 1–2 weeks during the summer swimming season
- After heavy rain or storms
- After higher-than-normal usage
- At the start and end of the swimming season
Common Mistakes to Avoid
- Shocking in daylight – UV light reduces chlorine’s effectiveness; always shock in the evening
- Skipping pH adjustment – Incorrect pH makes shock treatments less effective
- Swimming too soon – High chlorine can irritate skin and eyes
- Under-dosing – Too little won’t solve algae or bacteria problems
The Pool Chap’s Tip
Keep a small supply of pool shock on hand throughout the summer. In the UK, where weather can change quickly, it’s useful to treat the water after a sudden warm spell or unexpected downpour.
Final Word: Shocking your pool is a straightforward job, but getting it right will save you time, money, and frustration. With the right product, good timing, and a bit of testing, you’ll keep your pool safe, clean, and inviting all season long.
