Why do you want growth? Are you growing corals to sell? Trying to narrow that pH gap will send you down a rabbit hole and probably cost you one way or another (and not in a good way). I run a CaRx and dose kalk at night, but I honestly don't care about my pH swing too much and according to my apex/hydros in my two systems, it's a sizeable swing. Meanwhile, I have excellent growth and color. I don't chase numbers, I chase health. In my 40+ years of doing this, I've seen so many people chase numbers, only to spend stupid money, kill corals and fish, just because they're trying to get more growth. Why? There's a huge difference between a hobbyist's goals and a coral farm's goals. Increasing your growth by a few percentage points is meaningless (because that's about what it'll be by narrowing that gap), but to a farmer, that small percentage helps. We need to stop pretending we're farmers, when we're clearly not.
I'm all for creating stability in our systems, it can only help, but trying to alter things to narrow that pH gap seems like a waste of time and money, because if you do narrow that gap, it's not going to be a night and day difference. I think you would be better off fine tuning other aspects of your system that would achieve better growth than chasing pH, like feeding, trace elements, flow, lighting, etc......
Personally, I would put my energy elsewhere, but that's up to you.
