You should be okay with the Flagstone. There are some types of stone in Texas that it are reported that the salt degrades, but I don't know how true that is. The average running value for a Circupool SWCG (like I have) depending on model is about 3500 PPM of salt and they will run fine from 3000-4000 PPM. From a Google search: Seawater has a salinity of roughly 35,000 ppm, equivalent to 35 grams of salt per one liter (or kilogram) of water.
So literally you are looking at a 10th of the salt in sea water. Where you could potentially have more is if the water continually gets splashed on the flagstone, sits in puddles and then evaporates. But even then I don't hear much issue with it. Hosing it off once a week should be enough to completely mitigate this. My pool has has the SWCG for about 7 months now. I don't notice anything except for maybe a little LESS calcium scaling because of it. But I am also trying to keep my horrible Total Alkalinity down more to protect the cell, so that could be the real reason for less scaling now. I do have concrete pavers however.
We note that Texas pool builders in particular trash SWCG's. I suspect that is because they are much easier to take care of and have less problems over time. Can't sell you as much expensive service. And pools are expensive. No doubt about that.
I guess because I am 6'3" tall that 4.5' to me just isn't deep enough. I have a very small portion of my pool at 6' and I like it, honestly. If you are.. ahem... shorter.. 4.5' might be enough. Insurance companies don't like new pools deeper than about 7' but both 4.5' and 6' are okay. Maybe go five if you can, but not for the entire pool.
So for people adding salt for feel. That's it. It doesn't change the amount of free chlorine to CYA needed at all. It's kind of strange, and if you have time, read up in the pool school about all of this....
CYA holds chlorine ions in solution so they don't evaporate off as quickly. The more CYA you have the more free chlorine you need because the CYA snatches up those Ions. Any form of solid chlorine needs to be stabilized. They add CYA in every time. Once you hit about 120 PPM of CYA, you need so much chlorine to keep the pool sanitized you have to drain down and refill to lower it (since there is no real practical way to remove it chemically in any realistic time span.) So this is why TFP (and the BBB method) suggest to use bleach (or chlorine gas, either from a tank -- some services still do this -- or from a SWCG).. they are not stabilized. Bleach degrades to water and salt. I used my pool for 1/3 of a season and small amounts were added over the winter before I added the SWCG and my salt level was already at 800 PPM when I added the generator... so there are always tradeoffs no matter what method you use. Salt levels are one of the least damaging tradeoffs though in the grand scheme of things.... so in my case it would have taken just about 3 years to get to the 3500 PPM I am at now anyway. In comparison, most of my neighbors who use tabs generally are draining their pool every year and a half... and going higher than 3500 PPM of salt isn't bad for most pools... Note this doesn't matter what size pool you have because you have to proportionally add more bleach for a larger volume of water for the same FC levels.
Now the other part is the "balance" or "saturation index". This is almost completely separate from the CYA and free Chlorine. Enough to treat it separately in actual use. The salt does effect it a bit, but it's much less than Magnesium and calcium hardness, and this is why water softeners use salt for their ion exchange. The Pool Math program does take salt level into account and if anything it helps a little with scaling. But not much. You need to keep Calcium Hardness, Total Alkalinity, and pH in a balance... yes CYA matters in this a little too, but free chlorine does not. So there is a CSI calculation in the Pool Math app and on this website. You want to keep it as close to zero-- balanced as much as you can. If you have a SWCG it tends to make the water more alkaline, so a negative CSI is recommended. (Slightly Acidic).
It sounds complex but it's about once a week measuring those levels, putting it into a calculator and making adjustments when needed. It's not difficult. I encourage you to play with the calculators so you understand all of this. Even if you plan on having a service maintain the pool for you (which is completely unnecessary especially with a SWCG).
By the way.. you can always add the SWCG later. Honestly you can't add the salt to a newly plastered pool until 30+ days later... so you can do what I did. It was done in September. I added the SWCG myself (which is simple if you can do electrical work and PVC plumbing work) in May... No real issues at all with doing this. So you can think about it and get used to the other thrills about owning and managing a pool in the meantime. Doing it myself was $800. It was like $2.5K from the PB... for basically the same unit...
...... I won't be using it for exercise, but for cooling off after running or yardwork.
