Ozone is only effective within the cell, and doing absolutely nothing in the main pool vessel, as explained by Matt.
Within the SWG cell, you might have some benefit of a locally increased FC level, but that chlorine eventually ends up in the main pool vessel where it is still effective. That doesn't really have anything to with CYA. I am not so sure about the "super-chlorination" argument with SWGs in the first place. I once took a water sample with a syringe from within the return pipe and measured the FC. It was about 2-3ppm higher compared to the main vessel. Yes, the FC is higher in SWG-cell and return lines, but I wouldn't call it super-chlorination. I think it's more about the steady and reliable chlorine production of an SWG, as already pointed out by Newdude. (EDIT: I should add that this test was done with the SWG running at 100%, which I usually don't do, more like 50%. And my SWG regulates the chlorine output by adjusting the current and therefore the chlorine production per second, rather than the duty cycle as most US-models).
And yes, in older posts there were discussions regarding SWGs being more efficient with higher CYA levels, because the higher CYA might protect the freshly produced chlorine faster from UV. But as Newdude also already pointed out, this theory is no longer supported here.
@mas985 has done a number of tests over the years on the rate of chlorine decay by UV depending on the CYA concentration.
E.g. here:
Mark, Great experimenting (again)! waterbear also asked about water shielding UV but in the range where most of the destruction occurs, mostly for hypochlorite ion around 270-320 nm (see this link) and the low absorption of water in this same range (see this link), it would seem from your...
www.troublefreepool.com
here:
I know it's a bit late since you removed the SWG but I know why you had so many problems with it if your last water test is typical. Your stabilizer level is 30 ppm and that alone is enough to cause early cell failure and major pH problems leading to scaling and short cell life! This is why...
www.troublefreepool.com
and here:
Many years ago, I did a test of chlorine loss vs CYA level and published the results here: https://www.troublefreepool.com/threads/cya-testing-update.2984/ There were a few issues with the test that I wanted to resolve with some additional testing but never got around to doing it...until now...
www.troublefreepool.com
These tests have shown that the UV-protection increases with rising CYA-level more than one would expect by only taking the amount of Cl into account that is bound to CYA. The UV-extinction as the light goes deeper seems to play an important role. This results in smaller absolute chlorine losses at higher CYA levels when keeping the FC/CYA-ratio (and therefore the concentration of "active" chlorine, HOCl) constant. And because the steady and reliable chlorine supply of a SWG allows to run lower FC-levels, you can save even more FC from UV-destruction by running a lower FC level at the same FC/CYA-ratio, and basically run with SWG the same FC level at CYA 80ppm that you would run without SWG at CYA 40ppm.
This effect of better FC-protection at higher CYA-levels is generally also valid in non-SWG pools. But the higher CYA-level also increases the required SLAM-FC level, to the degree where the SLAM-FC of 31ppm at 80ppm CYA is getting very difficult to maintain. But with the steady and reliable chlorine supply of a SWG, the chances of slipping below min-FC and start an algae bloom are much smaller than in a manually chlorinated LC-pool. In an SWG-pool it's wort taking that risk and benefit from the reduced absolute chlorine consumption and extend the SWG lifetime. Without an SWG, the risk is not worth taking, sooner or later you will get distracted or run out of LC (especially in the current market), and there we SLAM again - but at 16ppm FC instead of 31ppm.
