How do you maintain your pH without dropping your TA? I thought adding muriatic acid dropped your TA, so wouldn't you need to raise it back up occasionally?
I automated my acid dispensing, which actually occurs once an hour! A tiny bit each hour. That keeps my pH very stable throughout the days, weeks, months. Which also keeps my TA very stable. I don't need to raise TA, because my fill water is high in TA. Indeed, I have to use a decent amount of acid to counter that incoming TA. I use less acid in the winter, because I add less makeup water each day.
But every pool is different, so you can only use the examples of others for rough comparison.
As Allen points out, small level adjustments (more often if necessary) work better than letting a level get way out of whack and then blasting it back. Since both my FC and pH are controlled by automation, they both get tiny adjustments many times a day. That keep FC, pH and TA very even, and none of them ever get way off. That's what works for my pool.
You mentioned you haven't tested pH in a couple weeks. Your fill water and pool usage will determine testing frequency, you can't really bend a pool's need for testing and dosing to your schedule, you have to follow
its schedule. Which you figure out from experience. How much pH and TA are coming into your pool, and how often, along with how many people are using your pool, and how often, (plus sun exposure and water features, etc) determine how often you have to dose to maintain levels. And as you mentioned, that'll change throughout the seasons. Adjusting pH every two weeks might work, but if it's not often enough, then you gotta dose more often. Simple as that. You'll figure out how long it takes for your pH to move that "0.3 - 0.4" that Allen mentioned, and that'll determine how often you'll need to test and dose. That might be every two weeks, or it might be every two days!
Now just to add another layer here, I have it in my head that a stable CSI is better for your pool finish than a fluctuating one. I figure, if there is an ideal CSI (and I believe there is) then the more time your finish spends subjected to that ideal CSI, then the longer it'll last, and the better it'll look. I can't back that up with hard data, just a hunch based on logic. That sounds like a contradiction to the previously mentioned advice of not sweating CSI as long as it's between -0.6 and 0.6, but it's not, really. I just choose to narrow that range, because I can, not necessarily because I have to.
It's why I added the automation. I test once a week, year round, but my dosing is occurring much more often. When my pH and TA and CH are stable, so is my CSI. So in addition to the automation, I adjust my CH once a year (via small water exchanges) rather than let it build up and up and up until it goes out of range. (Plus, my fill water has near-zero CH in it, because I fill my pool with soft water, to counter my high-CH fill water.) I took Allen's notion of "0.3 - 0.4" to a next level, and my levels never need even that much adjustment. I'm not suggesting you have to be that compulsive about it, it's not taught or normally done by most here, it's just my personal preference, and made possible by automation and my OCD!
I'll know in 20 years how this strategy pays off, if I need to pay $20,000+ for new pebble in 2045 or not. I'll let you know!
