Going back to the post asking about my specific pool. 20k gallons, plaster, about 3.5 years old, outdoors but screened in, SWG, with autofill. I have 6 deck jets, but typically these are only run one day a week for 15 minutes just to exercise the pump a little. No other water features or spa. Here are my numbers from testing this morning:
CL: 3 ppm (no CC)
pH: 7.8
Alk: 80 ppm
Ca: 310 ppm
Salt: 2900 ppm
CYA: 30 ppm
I know the CYA is much lower than recommended here, but my CL is well controlled at this level. Currently I'm only running the SWG from 10am to 3pm at 10%, but we're not using the pool yet. After we start using the pool in a week or so, I'll up that to around 8 hours, probably will up the percentage to 15% once it gets hotter. I run my filter pump continuously at 50%. I have tried running the system with Alk down at 60 ppm, but it didn't seem to make a lot of difference on my acid demand.
I did test the fill water by putting my filter/softener into bypass and drawing some water from an outdoor faucet near the water inlet after flushing it for a minute or so. CL was 1.2 ppm, ph 7.8, Alk 70, Ca 90. I have not noticed Ca creeping up (if anything I have to add some occasionally after we get a hard rain), and this tends to be a fairly humid area, so I don't think the fill has a big impact normally.