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Ozone wont work, and will quickly deteriorate the wood.Ozone, while a very powerful oxidizer, is only so, when it's ABSORBED into the water. In order for it to be absorbed into the water it has to have a long contact time with the water, and the water has to be pressurized. Ideally the contact time is 25+ seconds, and the water would be pressurized to at least two atmospheres. In your situation, the contact time would be about 1 second, and the water not pressurized at all. The ozone would bubble to the surface of the water, and being heavier than air would accumulate in VERY high concentrations, and deteriorate the wood above the water line. I saw a wooden hot tub, 3 years old, with this setup, and the wood above the water line had lost 1/2+" of thickness.
Moss can be killed effectively by copper ions, just as algae is prevented as well. So a copper/silver/zinc system would work and you could use non-chlorine shock (potassium monopersulfate, MPS) to oxidize the bather waste. The combination of silver ions and MPS is also an EPA-approved disinfectant (technically only in the Nature2 system since the EPA approves products, not chemicals). I don't know, however, if there are any problems with using metal ions in a wood spa.
No problem with metal ions in a wood spa...however, he has no pump, filter or circulation system of any kind.