It's still not a big change--if it dropped from 35 to 20 or 15 we'd be concerned, but from 35 to 30? That's OK.

Bromine is an alternate sanitizer to chlorine. It's more expensive, has a number of drawbacks, but is much more resistant to heat in hot tubs. It also doesn't "play well" with chlorine.

pH Up! is nothing more than Sodium Carbonate, aka Washing Soda, just overpriced.
3" chlorine tablets are Tri-chlor tablets--if they are 99% they are good. But for every 10ppm of chlorine they add, they add 6ppm of CYA/Stabilizer, plus push pH down.
Not sure what's in the Phos-Free, but I doubt there's any bromine in it.

Combined Chloramines can be all sorts of chloramines, not just the one bromine mixed with chlorine produces (monchloramine?) All kinds of things can be metabolized to form them, but guessing which one(s) caused the CC=3 is beyond me.