Warm water is a bacteria magnet. At 37–40°C, microbes thrive in the aerated environment of a hot tub. Left untreated, water quality can degrade fast. The formula for consistently clean, fresh-smelling water is simple: keep a gentle sanitizer program, filter every day, and stop contaminants before they enter.
The Sanitizer Landscape — values, benefits, and our stance
- Chlorine (informational only, not recommended)
- What it does well: fast, broad disinfection and easy availability.
- Why we don’t recommend it for hot tubs: stronger odour and by-products in hot, aerated water; many users find it harsher on skin and some components.
- Bromine (informational only, not recommended)
- What it does well: stays stable at spa temperatures and maintains a steady residual.
- Trade-offs: still a halogen program with characteristic smell and by-products; not our pick versus modern low-odour options.
- Chlorine dioxide (ClO2) — modern, low-odour power
- Benefits: powerful disinfection at low doses; excellent biofilm control; broad pH tolerance; low odour (no classic “pool smell”).
- How to use: start-up dose 1 tablet per 1,350 L with the pump running to establish a clean baseline; after heavy use, add a small top-up the next day.
- See our chlorine dioxide product page for details.
- Active oxygen / MPS (potassium monopersulfate) — gentle clarity maintenance
- Benefits: non-chlorine oxidizer that clears organics (sweat, oils, cosmetics) and restores sparkle; very low odour and skin-kind feel.
- How to use: weekly maintenance dosing per label; add a light “shock” the morning after parties or heavy use.
- How it differs from ClO2: MPS is mainly an oxidizer for clarity; ClO2 provides stronger, longer-lasting disinfecting and biofilm control. They work well together.
- See our active oxygen product page for details.
The routine we recommend:
- Start-up after a fresh fill: add 1 chlorine-dioxide tablet per 1,350 L with circulation on.
- Weekly: dose active oxygen (MPS) per label to maintain clarity.
- After gatherings: add a light MPS boost the next morning and extend filtration that day.
Filtration: the other half of clean water
- Daily circulation: run filtration every day (commonly 4–8 hours; more after heavy use).
- Keep the cover on when not in use.
- Media options: sand filters work; modern reusable filter balls are lighter, cleaner to handle, and can be machine-washed.
- Use a pre-filter: to catch larger debris before it reaches the main media.
Shower before you soak
A quick 30–60 second rinse removes sweat, lotions and cosmetics that would otherwise react with your sanitizer and cloud the water. It is the easiest way to reduce chemical demand and keep everything smelling fresh.
Quick weekly checklist
- After each soak: run circulation 10–15 minutes with the cover on.
- Weekly: add MPS; rinse the pre-filter; wipe the waterline if needed.
- As needed: machine-wash filter balls when flow slows or after messy weekends.
Bottom line
Skip chlorine and bromine. Start clean with one chlorine-dioxide tablet per 1,350 L, maintain weekly with active oxygen, filter daily, and make “quick shower first” a habit. That is how you keep hot-tub water crystal clear, low-odour and ready when you are.
