Many hot tubs and swim spas are offered today with an ozonator, a UV-C lamp or both. The expectation is often: fewer chemicals, less odour, less work. Part of that is true – but only if you understand what the systems can and cannot do. This article explains both methods soberly and helps with the assessment.
The basic principle: treatment in the plumbing
Neither ozone nor UV-C acts in the entire tub, only where the water flows past them – i.e. in the plumbing, usually after the filter. This is the most important point for the assessment: anything that happens in the tub, on the walls or on bathers’ skin is not directly reached by these systems. A sanitiser with a so-called residual effect in the water is therefore still needed, for example chlorine, bromine or an active oxygen system.
Ozone: how does an ozonator work?
An ozonator produces ozone (O₃) – either with a special UV lamp or by electrical discharge (corona method). The gas is introduced into the water via a jet (venturi or injector). Ozone is a strong oxidising agent: it breaks down organic contaminants such as sweat and cosmetic residues and acts against microorganisms.
What ozone does well:
– breaks down organic load that would otherwise “consume” sanitiser
– thus often reduces the need for chlorine or bromine
– contributes to clearer water and less of the typical “chlorine smell”, because less combined chlorine is formed
Limits of ozone:
– Ozone decays quickly and does not form a residual in the tub.
– The effect depends on how long and how often the ozonator runs – usually it is linked to the filter cycles.
– Ozonators age: lamps or electrodes and the check valves must be inspected or replaced according to the manufacturer’s specifications. An ozonator that has stopped working unnoticed is a common reason why chemical demand “suddenly” rises.
– Over time, ozone can put greater stress on certain materials; manufacturers select components accordingly.
UV-C: how does a UV lamp work?
In UV-C systems, the water flows through a chamber in which a lamp emits ultraviolet light in the UV-C range. This radiation damages the genetic material of bacteria, viruses and algae so that they can no longer multiply. No chemicals are added.
What UV-C does well:
– inactivates microorganisms in the water flowing through
– inhibits the multiplication of germs and algae in the water circuit
– works without adding substances and introduces no by-products into the water
Limits of UV-C:
– UV-C also only works in the chamber, not in the tub.
– UV-C hardly oxidises organic contamination – grease and cosmetic residues remain largely unaffected.
– The effect depends on lamp output, flow rate and water clarity. Cloudy water or a dirty quartz sleeve let less radiation through.
– The lamp loses output over time, even if it still glows. The replacement interval is stated in the manufacturer’s instructions.
Ozone and UV-C compared
| Feature | Ozone | UV-C |
|—|—|—|
| Principle | Oxidation | Radiation (inactivation of germs) |
| Breakdown of organic matter | yes | hardly |
| Effect against microorganisms | yes | yes |
| Residual effect in the tub | no | no |
| Typical maintenance | Check ozonator, injector, check valve | Replace lamp, clean quartz sleeve |
Because their strengths complement each other, some manufacturers use both systems in combination: ozone mainly deals with the organic load, UV-C with germs in the circuit.
Do ozone and UV-C replace water care?
No. Both systems are a supplement, not complete water care. A low but always measurable level of sanitiser in the tub remains necessary – because only it acts immediately where bathers enter the water. Likewise, pH and alkalinity must still be right, and the filter must be cleaned regularly.
Realistically, then: fewer chemicals, not no chemicals. Anyone interested in care concepts with as few additives as possible will find a detailed article on water care with fewer chemicals at the dealer Spa Natural, which classifies different approaches.
What to look for when buying
- What is installed? Ozone, UV-C, both – or only as an option? Ask specifically.
- How is it controlled? Does the system run only during filter cycles or continuously?
- Maintenance and spare parts: how often must the lamp or ozonator be replaced, and what does the spare part cost? This is part of the running costs.
- Monitoring: is there an indicator showing whether the system is working? Without one, only regular checks according to the instructions help.
Frequently asked questions
Can you smell ozone in a hot tub?
Directly at the inlet jet, a slight, characteristic odour can occasionally be noticed with the cover open. A strong or persistent smell is not normal and should be checked by service.
Can I retrofit an ozonator or UV-C lamp?
That depends on the model, the space in the equipment bay and the controls. Whether and how retrofitting is possible should be assessed by a specialist. DIY solutions are not recommended because of electrics and UV radiation.
Do I need to change the water less often with ozone or UV-C?
The systems can help keep the water in good condition for longer. However, dissolved substances still accumulate. Regular water changes therefore remain necessary, depending on usage and test results.
Fazit
Ozone and UV-C are useful building blocks for more pleasant water care in hot tubs and swim spas. Ozone mainly breaks down organic load; UV-C inactivates germs in the water circuit. Both relieve the sanitiser but do not replace it. Those who know this, keep to the maintenance intervals and continue to test regularly get the most out of them.
INFINITAS editorial team – in cooperation with the dealer Spa Natural, Hilden, Germany. Please refer to the relevant data sheet for which systems are installed in a specific INFINITAS model.