Hot Tub Water Care: A Step-by-Step Chemistry Guide

Hot tub water chemistry isn’t complicated once you have a system for it — but the order in which you do things matters a lot, and the wrong sequence is the reason most “I keep ending up with cloudy water” problems happen. This guide walks through the chemistry every Canadian Spa owner needs to know, in the right order, with the products we recommend and a few practical UK-specific tips.

We strongly recommend using Canadian Spa branded chemicals and maintenance products with your hot tub. They’ve been tested specifically with our spas and are designed to work safely with the materials and equipment inside. Chemicals can be bought individually or as part of our convenient Deluxe or Starter sets through our website.

We do not recommend salt water treatment systems for our hot tubs, as they can significantly degrade the internal components.

Choosing your sanitiser

Our preferred sanitiser is chlorine granules (di-chlor type) — it’s the easiest method to dose and control day to day, dissolves quickly, and works well across the range of UK water types.

Bromine in granular form is also compatible with our hot tubs, but it requires a bit more attention because it tends to gradually lower alkalinity, which in turn can pull pH down. Bromine is sometimes preferred by people with sensitive skin or strong opinions about the chlorine smell, but the trade-off is more frequent alkalinity adjustment. Our guide to why we recommend chlorine for your hot tub explains why chlorine keeps upkeep simple and when bromine is the better choice.

Skimmers are not recommended for hot tubs with capacities under 1400 litres, and where used they should be monitored to prevent chemical damage.

What each chemical does

Before getting into the dosing order, a quick reminder of what each product is for:

• Sanitiser (chlorine or bromine granules): kills bacteria and oxidises body oils, sweat and other organics. The main “keeping the water safe” chemical.
• pH adjusters (pH Up / pH Down): keep the water’s acidity/alkalinity in the right range (typically 7.2–7.6). Out-of-range pH makes sanitiser less effective and can irritate skin and eyes.
• Alkalinity Booster: raises total alkalinity (TA), which acts as a buffer to stop pH swinging around. Low TA is one of the most common causes of frustration with hot tub chemistry.
• Shock treatment: a larger dose used periodically (or after heavy use) to oxidise everything the sanitiser hasn’t.
• Foam reducer: a quick fix for the surface foam that can build up after a busy session. Doesn’t replace proper sanitisation.
• Test strips: measure all of the above. Use them regularly — see our test strips pack.

Why balance matters

Sanitiser levels are important — but pH and alkalinity matter just as much. Low alkalinity and an unbalanced pH can produce corrosive water that damages your hot tub over time, irritates skin and eyes, and makes the sanitiser less effective. All chemical concentrations should be tested regularly using test strips. If you have already noticed itchy skin or sore eyes after a soak, our guide to itchy skin and sore eyes after a hot tub walks through the usual causes and fixes.

If you use the hot tub frequently during the week, daily testing is best. Otherwise, weekly testing is enough. Water changes depend on usage, but we recommend completely replacing the water at least every three months — sooner for heavily used spas or holiday lets.

A quick note on UK water hardness

The UK has dramatically different water hardness depending on where you live. Hard water areas (much of the South East, East Anglia, parts of the Midlands) bring more calcium and scale considerations; softer water areas (Scotland, Wales, the North West) bring different challenges. If you’re in a hard-water area, scale management becomes part of routine chemistry — a small dose of scale inhibitor on each fill goes a long way. If your water is very soft, you may find pH and alkalinity drift faster. If your pH won't settle, our guide to why hot tub pH keeps changing walks through each cause. For dosing amounts and the early signs of build-up, see our guide to hard water and limescale in your hot tub.

The correct order to balance your water

Adjust your water chemistry gradually, in this order. The sequence matters — adjusting in the wrong order means you’ll undo what you just did.

1. Test current levels with a fresh strip.
2. Adjust alkalinity first.
   • If alkalinity is in range, skip to step 4.
   • If alkalinity is high, use pH Down (lowering pH gradually pulls alkalinity down too).
   • If alkalinity is low, use Alkalinity Booster.
3. Run the jets to circulate for 15–30 minutes, then re-test.
4. Adjust pH. If pH is in range, skip to step 6. Otherwise use pH Up or pH Down as needed.
5. Circulate again, then re-test.
6. Adjust chlorine or bromine if the sanitiser level is low.
7. Circulate again, then re-test.
8. Final check. If everything is in range, leave the hot tub cover open so vapours can escape, and run the jets for one full cycle (15–30 minutes). If anything is still off, adjust and re-test.

The whole process is usually 30–45 minutes start to finish, including circulation time.

Helpful tips

A few practical pointers that make ownership easier:

• Always follow the dosing instructions on each chemical container. Required doses vary depending on hot tub size, how often you use it and how much chemical is needed.
• Dose with the pump running so the chemicals disperse properly rather than settling on the shell.
• Wait between adjustments. Don’t add multiple chemicals at once and don’t dose, test, and immediately re-dose — chemicals need time to work.
• Shock the spa weekly in addition to daily/weekly testing — particularly if you’ve had several bathers in a short window.
• Use a separate, clean scoop for each chemical. Cross-contaminating granules can cause real problems.
• Store chemicals in a cool, dry place, well away from children and pets. Each container has its own safety guidance — read it.

For a hassle-free start, our Starter Hot Tub Chemical Kit includes everything you need: chlorine granules, foam reducer, pH Up, pH Down and 3-in-1 test strips.

Frequently asked questions

How often should I test the water?

Daily if you use the spa most days; weekly as a minimum for occasional use. Hot tubs in holiday lets or with multiple users should be tested daily without exception.

What’s a “shock” treatment and how often should I use it?

A shock is a larger dose of sanitiser (or a non-chlorine alternative) that oxidises contaminants the daily dosing hasn’t caught. Most owners shock weekly or after a heavy-use session.

Can I use chlorine and bromine together?

No — pick one and stick with it. Switching needs a full water change first.

My water has gone cloudy — what’s likely wrong?

Most commonly: low sanitiser, low alkalinity, or a dirty filter. Test the water, rinse the filter, and rebalance using the order above. If it doesn’t clear within 24 hours, contact our support team. If the water has also turned foamy or green, our cloudy, foamy and green water troubleshooting guide walks through each fix.

How long after dosing chemicals before I can get in?

Allow at least 30 minutes after adding any chemical for it to circulate fully, and check sanitiser is back in the safe range before getting in. After a full shock, wait at least an hour.

Does the Water Test app handle all of this for me?

Yes — the free Canadian Spa Water Test app calculates exact doses based on your spa’s water capacity and your current test strip readings. It’s the easiest way to get the chemistry consistently right.

Target ranges at a glance

Keep this table near your test strips. Always follow the dosing instructions on the container, or use the free Canadian Spa Water Test app for exact amounts.

Test	Target	If low	If high
Total alkalinity	80 to 120 ppm	Alkalinity Booster	pH Down, added gradually
pH	7.2 to 7.6	pH Up	pH Down
Free chlorine	1.0 to 1.5 ppm	Chlorine granules	Leave the cover open and the jets running, then retest. Do not get in until it is back in range
Bromine	As shown on your test strip and product label	Bromine granules	As for chlorine

Troubleshooting common water problems

What you see	Likely cause	What to do
Cloudy water	Low sanitiser, low alkalinity or a dirty filter	Clean the filter, balance alkalinity then pH, then sanitiser. Spa Clear can help gather fine particles
Foam on the surface	Body lotions, soap residue or old water	Shower before soaking, use Foam Free for a quick fix, shock the water and plan a water change
Strong chemical smell	Used-up chlorine combining with oils and sweat	Shock the water with Spa Shock and leave the cover open while the jets run
pH keeps drifting	Alkalinity out of range	Correct alkalinity first, then pH
Scale on the waterline	Hard water and high pH	Bring pH into range and wipe the waterline at each water change
Itchy skin or sore eyes	pH or sanitiser out of range	Stay out, test and rebalance before the next soak

Starting from a fresh fill

1. Fill through the filter housing using a hose with a pre-filter if you have one.
2. Switch on and let the water circulate before adding anything.
3. Test, then balance alkalinity, pH and sanitiser in that order, as above.
4. Shock the water once it is balanced.
5. Retest the next day before the first soak.

Can I use household bleach instead of spa chlorine?

No. Household products are not designed for spa water and can damage the shell, the pipework and the cover. Use spa-specific chemicals from our essential chemicals range.

Why do test strips give different readings?

Old or damp strips lose accuracy. Keep the lid closed, store them somewhere dry and replace the pot once it is past its date. Fresh test strips are inexpensive.

Should I adjust chemicals after a party?

Yes. Several bathers use up sanitiser quickly. Test the next morning, shock the water and rinse the filter.

One important note

Chemical damage is not covered under warranty. Using compatible, properly-dosed chemicals from the recommended range protects both your spa and your warranty. If in doubt about anything, contact our support team before adding anything to the water.