Chlorine Water Treatment

Pool & Hot Tub Chlorine Water Treatment

Chlorine water treatment means putting chlorine‑based sanitiser into your pool or hot tub to kill bacteria, algae and other harmful microorganisms. In the UK, chlorine remains the most trusted and cost‑effective method to keep water hygienic. With the right dose and regular upkeep, your pool and hot tub water stays clean, clear and safe.

Outdoor pools face extra challenges: intense sunlight (UV rays), leaves and organic debris, swimmers and temperature changes all work to reduce chlorine levels. That means you can’t just occasionally add chlorine - you must select the right type and maintain it properly day in, day out in Wales or elsewhere in the UK. 

Unsure why your pool is going green & eating chlorine? Visit our blog to learn more!

There are several popular forms of chlorine treatment, each with its own advantages:

• Stabilised vs non‑stabilised chlorine: Stabilised chlorine includes a UV stabiliser to protect the chlorine from breakdown by sunlight, which is ideal for outdoor pool chlorine treatment in the UK. But if stabiliser levels get too high, chlorine’s effectiveness falls. Non‑stabilised chlorine, such as calcium hypochlorite or liquid bleach - sodium hypochlorite, has no UV protection. It degrades faster under sunlight, but is excellent for shock treatments or when you need a rapid boost without adding more stabiliser.
• Tablets, granules and liquid forms: Tablets dissolve slowly and are great for regular, routine pool maintenance - releasing chlorine steadily over several days. Granular Calcium Hypochlorite chlorine (shock) is used to raise chlorine levels quickly when needed, for example after heavy use or storms - always dissolve granules in water first before adding to the pool. Liquid chlorine (sodium hypochlorite) is already dissolved so can be dosed directly; it’s useful for fast corrections, though being non‑stabilised it loses strength more quickly under UV exposure.

All Swim stock a complete range of both quality swimming pool and hot tub chlorine water treatment products, in addition to our own brand we also supply other major brands including Aquasparkle, Bayrol, Blue Horizons, Gold Horizons and HTH .

All chemicals are held in stock and are available for next working day delivery (UK mainland). Please note hazardous goods charges apply to certain items and these goods are only available on a two day delivery service.

Stabilised Chlorine Granules & Tablets

- Chlorine products with built‑in UV stabiliser that resist sunlight degradation, ideal for regular sanitising in both swimming pools and hot tubs. They dissolve at a moderate rate and help maintain consistent free chlorine levels over time.

Multifunctional Chlorine Tablets & Granules

- Combined formulas that include sanitiser, algaecide, and clarifier all in one dose, offering convenience and balanced water care. Especially useful when you want fewer separate chemical additions while keeping water clear and safe.

Liquid Chlorine

- A fast‑acting, chlorine in solution form that can be dosed directly into pools or hot tubs for rapid adjustment. It’s ideal when you need to boost chlorine levels quickly or respond to sudden demand without waiting for solid forms to dissolve.

Shock / Superchlorination

- High concentration chlorine used for intensive sanitising, such as after heavy bather load, storms, or algae outbreaks. These treatments quickly oxidise contaminants and reset water clarity, before returning to routine dosing.

If you are unsure of any element of water treatment or dosing our experienced team are always on hand to offer help and advice on all elements of regular water treatment or problem solving - for further help and advice please do not hesitate to contact us on either 029 20 705059 or alternatively complete our enquiry form.

Frequently Asked Questions (FAQ)

Q: How Often Should I Chlorinate My Pool?
A: In normal use, test free chlorine 2-3 times per week and add chlorine as required to keep levels between 1 and 3 ppm. Perform a shock dose every 1-2 weeks, especially after heavy rain, significant usage or fluctuations in water quality.

Q: What Is The Difference Between Free Chlorine And Combined Chlorine?
A: Free chlorine is the portion of chlorine available to sanitise water and kill microbes. Combined chlorine (also called chloramines) is chlorine that has already reacted with contaminants. A high level of combined chlorine signals that the pool needs shocking to oxidise those compounds.

Q: How Long After Chlorinating Can I Swim?
A: After applying a standard chlorine dose (routine maintenance with tablets, liquid or granules), wait 4‑8 hours, or until free chlorine levels drop into the safe range (typically 1‑3 ppm) and water chemistry (pH etc.) is balanced. After a shock dose (much higher chlorine concentration to deal with algae, contaminants or after heavy use), it’s safest to wait at least 24 hours, or until chlorine levels have fallen into the safe swimming range (1‑3 ppm), before swimming.

Q: What Happens If The Chlorine Level Is Too High Or Too Low?
A: If chlorine falls below around 1 ppm, bacteria and algae may grow. If chlorine exceeds ~5 ppm, it may irritate skin, eyes or equipment. In high chlorine cases, dilute water, aerate, or wait until levels drop into the safe range before using the pool.

Q: Do I Need To Add Stabiliser (Cyanuric Acid)?
A: Yes - in outdoor pools, stabiliser helps protect chlorine from being destroyed by sunlight. Aim for a stabiliser level around 30‑60 ppm. However, if stabiliser becomes excessive, it can reduce chlorine’s effectiveness, so avoid over‑stabilising.

Q: How Do I Clear A Green Pool?
A: To clear a green pool (usually caused by algae), follow a systematic process:

1. Test and balance water chemistry (pH, alkalinity, stabiliser) so chlorine can work effectively.

2. Brush all surfaces (walls, floor) to dislodge algae into the water.

3. Apply a shock dose of chlorine (often 2‑5× normal dose depending on severity).

4. Run your filter continuously to remove dead algae and debris.

5. Vacuum and backwash/clean the filter regularly during this process.

6. If water remains cloudy or green, repeat shock dosing or consider using a clarifier or algaecide as a supplement.

7. After clarity is restored, retest water and maintain free chlorine in the 1‑3 ppm range and pH in the ideal range to prevent recurrence.

For further help and advice on both preventing a green pool and clearing it once it has turned green, please visit our blog!

Chemicals and Water Management

All Swim has produced a complete guide to swimming pool and spa water management. The aim of this guide is to explain step by step, the principles of maintaining safe high quality water with the minimum amount of expense and effort. The guide contains advice on general maintenance and chemicals. You can view the complete guide to water management here.
Note: The recommendations in this guide are for domestic swimming pools and hot tubs only.

Swimming Pool Chemical Safety

• Read instructions on each swimming pool chemical product thoroughly before use
• Never mix different swimming pool chemicals
• When pre-dissolving chemicals, always add chemicals to water and never vice versa
• Always pre-dissolve chemicals in a clean plastic container
• Always handle your swimming pool chemicals in a well-ventilated area, preferably outdoors
• Never use unlabelled swimming pool chemicals
• Store all swimming pool chemicals in a secure, dry and cool place
• Keep chemicals away from children and animals
• Avoid spillage
• In the event of a spillage, clean up using clean receptacles and dispose of in the pool. Flush area thoroughly with a large volume of fresh water
• Before disposing of empty containers, rinse them thoroughly in the pool
• Always wash hands after handling pool chemicals