I am not disagreeing with you on the need to keep more than 2PPM of chlorine in the pool, thank you for teaching me that. 3 turns per day is what my PB recommended, I don't think it'll hurt anything, but you're right, I can probably back off on that.
Regarding the UV though,
the main peer-reviewed academic paper on UV sanitizers that Chem Geek refers to (link) is one that I found independently, that I have read, and I have drawn a different conclusion to Chem Geek.
- When turned on for 12 hours per day, I calculated that my unit gives double the UV-C dose (fluence) that is recommended by UV disinfection regulations to produce 4 log kill of microorganisms (99.99%) in water purification applications.
Link here for the 4 log kill. Actually it's way more than 4 log kill for most microorganisms. It's not undersized.
- Using the same paper that Chem Geek referred to, I calculate my loss of free chlorine to be 0.06ppm per day due to the UV unit
- My actual experience, having this UV unit on for 12 hours per day, is that my total free chlorine loss is less than what most people experience
In that other post, Chem Geek's premise against UV sanitation is that there is *some* dissociation of HOCL at the 254nm UV-C wavelength, and he's right, it is non-zero. However, it's the amount that is important, and in the very diagram that Chem Geek refers to, it clearly shows the dissociation of HOCL by UV-C is about 20% of that of UV-A that comes from the sun. There's also a *lot* more UV-A hitting the pool.
The final conclusion of that very same paper is that "The decomposition of free chlorine depends on the pH, concentration of free chlorine, fluence, and water quality. At fluence of 400 J/m2, the decomposition of free chlorine is very slight (∼1%) in DI water when the concentration of free chlorine is not very high (∼20 mg Cl/L)."
The fluence (UV dose applied to the water) of my unit, being on for 12 hours per day, is about 800-900 J/m2 (see my other post for my calculations), that being double the dose normally recommended for UV disinfection regulations. So you can't say it's undersized. At that fluence, I calculate that I'm losing 0.06ppm of chlorine per day due to the UV light, which closely matches my actual chlorine consumption of around 0.5ppm per week all things considered (sun, leaves, etc).
So:
- My unit gives double the UV-C dose (fluence) that is recommended by UV disinfection regulations
- Using the same paper that Chem Geek referred to, I calculate my loss of free chlorine to be 0.06ppm per day due to the UV unit
- My actual experience, having this UV unit on for 12 hours per day, is that my total free chlorine loss is less than what most people experience