Re alk controller, you said it has some risks. Such as????
Alk controllers are new. The probe must be cleaned and calibrated. It can go out of whack and cause an alk swing. This, unlike normal pH swings, is harmful. Also... and this is the key... adding alkalinity is not a good way to control pH. You'll end up with high alkalinity and still have pH swings. If you want a controller to control alk (the important parameter), I'm all for it. Just know it needs maintenance and won't really help with pH.
...pH is cycling between 7.87 and 8.1 per Apex, with lighting cycle.
That range is just fine. With elevated CO2 levels in our homes due to better seals and insulation it is really the new normal. A CO2 scrubber can help but isn't necessary.
Tank is still somewhat newish...
Hair algae is an expected event in a new tank. Manual removal, working on nutrient levels, and competition (Algae scrubber, cheato, etc.) are good ways to keep it in check until the tank matures. Don't expect miracles from a scrubber though. Everything takes time.
Nitrate (per salifert drops and dipstrip (feh!)) are 0
There are nitrates in the system. Most of it is bound in the hair algae and not available to your test kit. Not a bad thing, just the way it works. You can't test accurately for free nitrate when there is a lot of algae in the tank.
... (per ATI drops test) has been at 8 or so (though resolution isn't great with that test; plan to get a Hanna). Calcium (per ATI drops test) has been at 380 (same note re resolution).
8 dKh and 380 ppm are ok. 420+ would be a little better. With little in the tank to use it (SPS, LPS corals, & Coralline), calcium & alk shouldn't need much 2 part at all. Also, you could be actually lowering you alk & calcium by adding too much two part. It may be cause precipitation events that cause the calcium and carbonate/bicarbonate to fall out of solution as calcium carbonate. You also need to watch magnesium. Without it, you will have trouble maintaining calcium levels.
Re chasing pH, generally speaking I think it's sage advice not to go chasing things seeking a "perfect" number. That said, it is one indicator that does seem to swing more than would preferred. Although alk stability seems to be more important from what I've seen/read, pH is more readily ascertainable for me (Apex Fusion app).
Stable Alk is very important. Chasing pH will lead you astray. Watching it is ok as an indicator, but trying to make it stay at a predetermine level is not a best practice. Day/night swings are natural. It's ok if something that is otherwise beneficial reduces the swing, but I wouldn't spend a penny on anything to directly control pH.
Re algae scrubber, as noted above, it should remove nutrients naturally. Also, I am thinking that it will outcompete the nuisance algae I've still got and help get rid of it. So that's another reason I was leaning that way.
Good choice, IMO. Just remember, it takes time.
I plan to add Neptune DOS/DDR at some point, but don't have enough coral in there now to justify it -- just the few pieces I xferred over from the 22, which seem to be thriving/growing (SPS)/way opening up (ACAN)
The corals from your 22 might not need als/calcium supplementation in the big tank for now. There may be way more available calcium carbonate for their growth that they need. Water changes might suffice for quite a while. I would stop adding two part and definitely stop the Purple UP (Trash it). Do some normal water changes, let the tank stabilize, then test for alk, calcium, AND magnesium, and go from there.
Speed kills. Take your time.