By the SwimSpaHub UK – Expert Reviews, Guides & Best Prices Team · Updated May 2026 · Independent, reader-supported

Swim Spa Chemicals Guide UK – What You Need & How Much It Costs

Maintaining a swim spa doesn't require a chemistry degree, but understanding your chemical options will save you money and keep your water crystal clear. Whether you're new to swim spas or upgrading from a traditional hot tub, this guide breaks down what you actually need, what each system costs, and which approach suits your budget and lifestyle.

What chemicals do swim spas actually need?

All swim spas require three core chemical functions: sanitisation, pH balance, and alkalinity control. Sanitisation kills bacteria and algae. pH balance (ideally 7.2–7.6) keeps the water comfortable and protects equipment. Alkalinity acts as a pH buffer, preventing wild swings when you add other chemicals.

Beyond that, you may need clarifiers, calcium hardness adjusters, and test strips. The specific products depend on your chosen sanitisation method.

Chlorine systems

Chlorine is the most straightforward and familiar option. It's potent, affordable, and proven over decades.

How it works: Chlorine (whether tablets, granules, or liquid) oxidises contaminants and maintains a residual that keeps killing bacteria between doses.

Pros:

• Cheapest upfront and ongoing
• Fast-acting; visible results
• No special equipment required beyond a basic feeder or floater
• Widely available at every pool shop and supermarket

Cons:

• Creates chloramines (the harsh chemical smell), which irritate eyes and skin at higher concentrations
• Requires more frequent testing and adjustment
• Some people report sensitive skin reactions

Monthly cost: £15–30 for an average 6–8 person swim spa, depending on usage and water quality.

Bromine systems

Bromine is gentler than chlorine and particularly popular with people who spend hours in their spa regularly.

How it works: Bromine tablets dissolve slowly in a feeder. Unlike chlorine, bromine doesn't break down as quickly when exposed to UV light, making it steadier in outdoor spas.

Pros:

• Milder on skin and eyes than chlorine
• More stable; needs less frequent adjustments
• Doesn't create the harsh chlorine smell
• Excellent for warm water (spas naturally suit bromine)

Cons:

• Costs 20–40% more than chlorine
• Slower to react if contamination spikes
• Requires a compatible feeder system
• Slightly more complex chemistry when balancing alkalinity

Monthly cost: £25–45 for an average spa, depending on climate and user frequency.

Saltwater systems

Saltwater (salt chlorine generator) systems convert salt into chlorine on demand, using a small electrical cell.

How it works: You add pool salt to the water, and the salt cell generates free chlorine continuously. It's an automated, gentler approach.

Pros:

• Low chlorine smell; much softer water feel
• Minimal chemical handling—no daily tablet or powder additions
• Lower per-use cost once the system is installed
• Ideal if you use the spa regularly

Cons:

• Higher upfront cost (£800–2,000 for the cell and installation)
• Cell requires replacement every 3–5 years (£400–700)
• Salt can corrode non-stainless fittings if not managed
• Requires occasional pH and alkalinity monitoring
• Not ideal for intermittent users or small spas

Monthly cost: £5–15 in salt and testing, plus amortised cell replacement. Works out cheaper long-term if you use the spa regularly.

Monthly cost breakdown

Here's what you're realistically spending:

Chlorine: Tablets (£10–15), test strips (£3–5), stabiliser if needed (£2–3). Total: £15–30.

Bromine: Tablets (£20–30), test strips (£3–5), alkalinity adjusters occasionally (£1–2). Total: £25–45.

Saltwater: Salt (£2–5), test strips (£3–5), cell replacement amortised across 4 years (£100–150 annually, roughly £8–12 monthly). Total: £13–22 monthly plus £400–700 every 4 years.

These figures assume a 6–8 person spa used 3–4 times weekly in a typical UK climate. Heavy use or poor water quality increases costs.

Testing and maintenance

Whichever system you choose, weekly testing is non-negotiable. Test strips are cheap and reliable; digital test kits offer more precision but cost £30–80. Aim for:

• Free chlorine: 2–4 ppm (bromine: 3–5 ppm)
• pH: 7.2–7.6
• Alkalinity: 80–120 ppm
• Calcium hardness: 150–250 ppm

Weekly water changes (10–20% drain and refill) keep total dissolved solids down and reduce chemical buildup.

Which system should you choose?

Go chlorine if you're budget-conscious, use the spa occasionally, or want the simplest approach.

Choose bromine if you use the spa regularly and prefer softer water and fewer chemical smells.

Invest in saltwater if you're a frequent user, want minimal hands-on maintenance, and can handle the upfront cost.

Getting started

Buy a complete starter kit—these include everything: sanitiser, pH plus/minus, alkalinity increaser, test strips, and basic instructions. Costs range from £25 (chlorine kits at supermarkets) to £60 (premium bromine kits from specialist suppliers). It's the most cost-effective entry point and ensures you have the right ratio of chemicals.

Never guess at dosing. Overdosing sanitiser can cause skin irritation and accelerate equipment wear; underdosing invites algae and bacteria. Follow the kit instructions carefully, usually dosing by water volume.

Good water chemistry takes 10 minutes weekly. Stick with it, and your swim spa will stay crystal clear, comfortable, and ready whenever you are.