Active oxygen in the pool: benefits, limits and combinations

What "active oxygen" is

Two main categories of product are sold under this name. The first is potassium monopersulfate granules, an oxidizer that "burns off" organic pollution in the water. The second is liquids based on hydrogen peroxide, usually sold together with an "activator" or an algaecide. Peroxide eventually breaks down into water and oxygen, while monopersulfate leaves sulfate salts behind. Neither of them forms chloramines.

The difference from chlorine is fundamental. Chlorine oxidizes and disinfects, and it stays in the water as a measurable free residual that protects the next swimmer. Active oxygen acts mainly as an oxidizer and for a shorter time, which is why systems based on it need more frequent additions and a schedule you actually stick to.

What you gain

• Hardly any smell and less irritation: without chloramines, eyes and skin are less bothered, something people with sensitivities appreciate.
• No stabilizer build-up: there is no cyanuric acid creeping up year after year, as happens with stabilized chlorine tablets.
• Quick return to the water: after adding oxygen granules, you can usually swim again soon, as the label specifies.
• Useful as a supplement too: monopersulfate granules can also go into a chlorine pool, to oxidize pollution after heavy use without raising the chlorine.

The limits of the method

Active oxygen struggles when the water is under a heavy load. In a Greek summer, that means more care than some packaging suggests.

• Warm water: as the temperature rises, especially above about 28 °C, peroxide breaks down faster and algae get their chance. See how water temperature affects the chemistry.
• Many swimmers: at a party or in a full house, the residual is used up quickly.
• Testing: chlorine kits do not measure it; you need special strips. In addition, monopersulfate can interfere with the DPD total chlorine test and show falsely high combined chlorine. More in how to test pool water.
• Incompatibility: hydrogen peroxide and chlorine neutralize each other. If you switch from chlorine to peroxide, wait for the chlorine to drop first.
• Holiday rentals: for shared-use pools, health regulations usually require a measurable residual disinfectant. Before choosing something other than chlorine, ask your engineer and see the rules for pools at rental properties.

What to combine it with

In practice, active oxygen works best as part of a system rather than on its own.

For the last two, see UV disinfection and ionization. Whichever system you choose, pH stays critical: keep it at 7.2–7.6, because outside that range every disinfectant works less well and the liner is put under strain. If your main complaint is the smell, first look at the causes of chlorine smell; it can often be solved without changing method.

Never mix oxygen products with chlorine or other chemicals in the same container. Dissolve the granules in a bucket of water and pour the solution near the return inlets with the pump running, never concentrated onto the liner.

Questions

See also