Before getting into each alternative, one concept needs to be clear: some disinfectants have residual protection, they keep working in the water after being applied, while some systems only act at the moment the water passes through them, leaving no protection behind afterward. That difference is the key to understanding why many of these alternatives get combined with each other instead of used alone.
Does it keep protecting the pool water?
Bromine
Bromine is a chemical cousin of chlorine and works in a similar way: it disinfects and leaves some residual protection in the water. Its strong point is that it performs better than chlorine in hot water, which is why it's the usual choice for spas and heated pools at high temperatures. Its main limit is that it breaks down faster than stabilized chlorine under sun exposure, which makes it less practical in large outdoor pools, where it would get used up quickly and drive up maintenance costs.
Ultraviolet (UV) light
A UV system runs the water through a chamber with ultraviolet light that inactivates bacteria, viruses and, in particular, certain chlorine-resistant microorganisms. It's a very effective treatment as a complement, and it significantly reduces the chemical disinfectant load needed. Its limit is that it only acts at the moment the water passes through the chamber, it leaves no residual protection in the pool itself, so it can't be the only line of defense: any contamination that enters after that point stays untreated until the next pass through the filter.
Ozone
Ozone is an even stronger oxidizer than chlorine, generated by a specific piece of equipment and injected into the filtration circuit. It's very effective at oxidizing organic matter and microorganisms, and usually leaves the water with a characteristic sparkle. It shares the same limitation as UV: it breaks down very quickly and leaves no residual protection in the pool water, so it's almost always combined with a reduced dose of a disinfectant that does provide that ongoing protection.
Active oxygen (oxygen-based systems)
Active oxygen-based systems are a gentler option, without chlorine's characteristic smell and with less impact on the skin and eyes of sensitive users. It's a popular alternative for small pools, spa pools and domestic hot tubs. Its main limit is that it needs to be dosed more frequently than chlorine to maintain constant protection, and its disinfecting power against certain microorganisms is more limited than chlorine's in larger or heavily used pools.
The most practical base for most pools
- Constant residual protection
- Predictable cost and maintenance
Good complements, not always self-sufficient
- No residual protection (UV and ozone) or more frequent dosing (active oxygen)
- Usually need a supporting disinfectant
Why we still recommend chlorine or salt for most pools
For most of the pools we maintain, we still recommend traditional chlorine or salt chlorination as the base treatment, and not out of habit: it's the combination that best balances constant residual protection, reasonable cost, good UV resistance when used with stabilizer, and maintenance that doesn't require checking the system every day. That doesn't mean the alternatives are bad, bromine makes sense in a spa, UV and ozone are excellent complements for reducing odors and chloramines, and active oxygen can be enough for a small, occasionally used pool. It means that, for the most common case of a community or residential pool in the south of Madrid, chlorine and salt still give the best result with the fewest complications. If you're unsure which suits you better, we have a specific comparison in chlorine vs. salt: which to choose.
Frequently asked questions
Can I have a pool without any chlorine at all?
It's possible, especially in small pools or spas using active oxygen, but most standard-sized pools generally need some disinfectant with residual capacity, chlorine, bromine, or indirectly salt chlorination, because systems like UV or ozone leave no protection in the water once it has passed through the equipment.
Do ozone or UV completely replace chlorine?
Not entirely. Both are very good oxidizers and greatly reduce the microorganism load and the chlorine needed, but they don't leave residual protection in the water. That's why they're usually combined with a reduced dose of a disinfectant that does leave one.
Why does D'Martinez recommend chlorine or salt in most cases?
Because it combines something the alternatives don't achieve all at once: constant residual protection, reasonable cost, good UV resistance with stabilizer, and easy maintenance. That doesn't mean bromine, UV, ozone or active oxygen aren't good solutions in the right case.