For refill due to evaporation I'd grab that hose from the car washing and fill the pool as it won't let the CH climb any higher.
You're making me feel like all that extra work to hard-plumb the pool into my irrigation was a waste of effort!
I just went on a short bender, looking at ion exchange filters, figuring I might add one to the line feeding the pool. But the ones I found are rated just 2000 - 2500 grains, meaning only ~150 gallons at my 15 gpg hardness. I do 300 gallons per inch, when topping the pool, so that's a no-go.
What's the target and acceptable maximum CH for a vinyl pool?
Nothing like the desert where they replace more than their pool volume each year.
Dang! Didn't even think of that. Yeah, I add 1" (~300 gallons) just a handful of times per summer. We have crazy high humidity, so evaporation is lower. Other than our typical seasonal drought July 1 to Aug. 15, we usually have enough rain that we're dumping rather than filling.
I had 4" of rain in two days this past weekend, and it's cool now, but this was preceded by two weeks of 90 - 100F with no rain. Just our usual summer ups and downs.
You'll fluctuate because it'll rise a little during dry spells but then wet spells will level it out with overflow. At the end of the season it should be relatively neutral.
Excellent.
On the whole 'timer' thing - You may want to consider something like a Smart Outlet instead - you can set schedules for them just like a timer, plus control them from your phone (and check their status).
Our whole house is automated via ZWave, we have literally dozens (plural) of those outlet modules and smart switches for outside lighting, etc. I also have one plugged into the utility receptacle, which you might be able to see thru the clear cover in the photo I posted, which controls string LED globe lights on the fence. I like this system, because it's integrated into our home security system, all in one app with automation, and everything down to water flood sensors and corresponding triggers for shutoff valves (eg. blown washer hose will never flood our house).
Trouble is, with that pool utility panel so far from the house, and our 2 ft thick stone walls, it's not exactly reliable. I installed a repeater near a 4th floor window, which seems to have the best line of sight down to that panel, which is blocked from the house by the pool wall itself. That has helped, but still not totally reliable. Might be easier to toggle the 50 amp mains out from the house, as that could all be arranged in the basement with a contactor, and more reliable comm's. But of course, that'd be killing everything, including some of the outside lighting.
I may look into more Zwave repeaters, or maybe even installing an outdoor WiFi router for better internet access at the pool (streaming sound system). But to be honest, a mechanical timer could probably work just as well for me. I don't need the automation for monitoring, as I also have full circuit monitoring of four of our seven breaker panels, via multiple Emporia Vue systems. I didn't put a Vue in the pool panel, it's such a tiny panel, but I have it on the feeder going out to that panel, so I can see total pool usage. By amount of draw, I can tell whether just pump or pump + heater is running, at any time.
Yeah... I have
seven breaker panels.

Big old house, roughly 8100 sq.ft and 300 years old., nothing here is straightforward.