IDOL SPAS · advice center
Chlorine-free hot tub maintenance with GUAa: a complete step-by-step guide
Chlorine is the most widespread way to keep hot tub water clean — but it is also why some people find that their hot tub “smells like a swimming pool”, irritates their eyes or skin. Chlorine-free maintenance based on active oxygen is a convenient alternative: it keeps the water fresh by oxidizing impurities, without the smell of chlorine. In this guide, you will find the exact procedure using the Czech GUAa OxiSystem, which we keep in stock in our online shop — including what active oxygen cannot do and how to address it.
For a solid-shell tub, the material and surface care are also important; find out more in our overview of acrylic hot tubs.
How GUAa OxiSystem works
The system has two complementary components:
- GUAa OXI — active oxygen (based on oxygen-containing potassium salts). It oxidizes organic impurities in the water — perspiration, cosmetics and skin oils — the “food” that would otherwise cause the water to deteriorate. It works quickly: you can bathe just one hour after application.
- GUAa WHIRLPOOL — a supplementary water care product: it helps substances disperse evenly throughout the water column, limits the formation of a surface film and reduces the build-up of impurities on the tub walls.
An honest explanation of what this system is not: active oxygen oxidizes impurities; it does not sterilize the water. For chlorine-free maintenance, we therefore recommend a UV-C lamp (it is fully compatible with GUAa — we offer it as an equipment option), thorough filtration and regular water replacement. This exact combination makes chlorine-free operation practical — and this is precisely how we configure it in our hot tubs.
Commissioning (fresh fill)
- Mechanically clean deposits and limescale from the tub (when changing the water, SPA DECALCIT will help).
- Fill the tub and switch on the filtration circuit.
- Adjust the pH to 6.8–7.4 (drop tester + pH Minus/Plus). Please note: with GUAa, the target pH is slightly lower than the usual 7.2–7.6 — OXI has a mildly acidic effect, and the system is designed accordingly.
- Apply OXI: 50 g per 1 m³ of water while filtration is running (dissolve it in a bucket of warm water and distribute it across the surface).
- After 12–24 hours, add the initial dose of WHIRLPOOL: 250 ml per 1 m³.
- Once mixed, the hot tub is ready; after 7 days, switch to routine maintenance.
Weekly routine (repeat every 7–14 days)
Step: 1
What: Measure and adjust the pH (check every 2–3 days in summer)
Dose per 1 m³: target 6.8–7.4
Step: 2
What: Apply OXI across the surface with filtration and jets running
Dose per 1 m³: 50 g
Step: 3
What: After 12–24 h, add WHIRLPOOL directly to the tub
Dose per 1 m³: 100 ml
Step: 4
What: Rinse the filter cartridge
Dose per 1 m³: —
A practical tip: one level cap from the OXI container ≈ 100 g. For a typical hot tub with a volume of ~1 100 l, use half a cap of OXI per week + ~110 ml of WHIRLPOOL. If the water foams after a party, a defoamer will help (10 ml/m³ as needed).
Annual maintenance plan
Frequency: Daily/every other day
What to do: visually inspect the water; check the pH every 2–3 days in summer
Frequency: Weekly (7–14 days)
What to do: pH → OXI → WHIRLPOOL after 12–24 h; rinse the cartridge
Frequency: Monthly
What to do: check alkalinity (target 80–120 mg/l), deep-clean the cartridge (SPA CLEAN FILTER)
Frequency: Every 3–4 months
What to do: clean the circulation circuit (before draining, with the tub full: add the product to the circuit, run the jets for ~10 min, drain and flush) → complete water replacement → descale → refill with the initial dose
Frequency: Seasonally
What to do: inspect/replace the filter cartridge (every 3–5 months), check the technology — our service team will be happy to help
Filtration: run 2–3 shorter cycles each day so that each cycle filters the entire volume of water (duration = volume ÷ filtration capacity). When you are away, err on the side of more filtration — stagnant water deteriorates faster.
What never to do with GUAa
- Do not mix it with chlorine or bromine. The manufacturer explicitly warns that GUAa products must not be used together with chlorine-based products.
- Do not combine it with a saltwater system — electrolysis produces chlorine; see the previous point.
- Do not switch from chlorine overnight. The correct procedure: either neutralize the chlorine with OXI (it breaks down in approximately 30 minutes after mixing), replace 30–50 % of the water, or leave the circulation running for 1–2 days without adding chlorine. Start using GUAa no sooner than 1–2 days after the last chlorine dose.
- Do not rely on chemicals when the filter has been neglected. The cartridge is the first line of defense in chlorine-free operation — hence the emphasis on rinsing and cleaning.
Frequently asked questions
What role does GUAa play in water care?
GUAa OxiSystem is chlorine-free oxidative water care: active oxygen breaks down organic impurities, while WHIRLPOOL keeps the water clear and the surface free of film. Enhance the water’s microbiological protection with a UV-C lamp, thorough filtration and regular water replacement — this is exactly how we recommend chlorine-free operation.
How soon after dosing can I bathe?
After applying OXI, one hour with filtration running is sufficient. WHIRLPOOL is added 12–24 hours after OXI.
Why does GUAa use a different pH from the “swimming pool” range of 7.2–7.6?
The system is designed for a pH of 6.8–7.4 — OXI has a mildly acidic reaction and works best within this range. Follow the manufacturer’s values, not general charts.
How often should I change the water?
For a private hot tub, every 3–6 months (sooner with intensive use); with GUAa, we recommend combining a 3–4-month cycle with cleaning the circulation circuit. Topping up part of the volume monthly helps between changes.
What if the water becomes cloudy or foamy?
Cloudiness: check the pH, clean the cartridge and apply an extra dose of OXI; a clarifier will also help (SPA CLARIFICATION). Foam after intensive bathing: use 10 ml/m³ of defoamer. If nothing helps, it is time to change the water.
Can I use GUAa in a hot tub from another brand?
Yes, the system is not limited to our tubs — it is dosed according to the volume of water. However, for hot tubs with their own automatic water treatment system (salt, chlorinator), seek advice first; these systems cannot be combined.
Is chlorine-free operation cost-effective?
The costs are comparable to chlorine-based maintenance (on the order of hundreds of Czech crowns per month, depending on volume and use) — the main benefit is comfort: odor-free water that is gentle on the skin and eyes. You can calculate the total operating costs in our article on how much it costs to operate a hot tub.