I have a similar set up (liquid chlorine with a Pentair Intellichem system as well as the Pentair UVBioshield system. I too have had the same question as I have NOT added anything like CYA to the pool and thus far have had no issues. The water looks very clean and clear though the chlorine levels do seem low all the time 0.5ppm.
What am I missing??
I should have clarified. I was not trying to say that it looked beautiful as in healthy. It is just a stunning pool. It really is beautiful. Lots of glass tile and the water was crystal clear. But I assume that pic was taken right after being filled for the first time. If you find my other posts on this thread you will see that I am absolutely in the pro-CYA camp.
And I was just attempting to add that clarification, for the OP, not necessarily for you. If you practice TFPC, it doesn't really matter if you understand that concept or not. Your water is safe. But the OP is looking to modify TFPC and so (I think) we're all trying to help him understand what is involved in attempting that. For example, just tweaking his FC level to clear up that errant bit of algae is not assurance that his pool is properly sanitized. TFPC works hand in hand with the FC/CYA levels to allow not only enough chlorine to sanitize a pool, but also provide an additional amount, in a buffer, to cover un-planned-for attacks on chlorine (from intense sun days or heat or bird fly-over or dead rodents or a peeing guest or whatever). Things that happen to outdoor pools regularly. So yes, he can probably figure out an FC level that will make his pool
look good, and even sanitized for periods of time, but not necessarily one that will keep the water safe for his family all the time.
My take away from my studies: No body of water intended for swimming is 100% safe, and I doubt it can be made so. To be graphic, it'd be pretty easy to swim through and/or ingest something harmful if you happen to catch it just right (bird poop, baby pee, whatever), but in a TFP pool those incidents would be very rare because we all have enough chlorine in our water to negate something like that quickly. And likely enough to negate multiple attacks, should they happen at the same time. But the OP wants to run the required amount of chlorine very "close to the edge," virtually teetering on sanitized/unsanitized, so close that he's thinking of supplementing sanitation with ozone and UV and what all else, which don't work all that well on the examples I just listed, not anywhere near as fast anyway. He's likely going to have more "crud" in his water more of the time, and he won't know it's in there just by looking at his water clarity or checking for algae (which is the motivation for chiming in about your comment). Yes, he might have solved his algae problem for that day or week, but he likely won't have enough chlorine in his pool some part of the time to handle all the things that need to be sanitized. He'll need to rely on the nasties finding there way to the ozone chamber or UV chamber (if I'm understanding correctly how they work). That ozone won't be attacking anything out in his pool, not like enough chlorine would. So every time he gets in his pool, his odds are going to be much higher than yours or mine that he's going to run into something undesirable. Whatever as-yet-to-be-clearly-defined reason his wife has for insisting on this risk, is, well, not worth the risk.
I've put my faith in TFP. Are there alternate ways of sanitizing a pool? Yes. Has anyone found a way to do it better than TFP? Not that I know of. Do I have confidence that one person, experimenting with one outdoor pool, is going to find a way to do it properly without CYA? No, none at all.
Sorry AJB, I don't mean to offend you. I think you're chasing the wrong rabbit. IMO, you and your family would be better served by you spending your time proving to your wife that CYA is safe enough, instead of trying to find a solution to something that doesn't need to be solved...