Thanks all, and hello fellow tucsonian. I wish I had a spa spillway, I just have a 4x6" overflow vent from the spa to the pool, which I overaccounted for initially, and ignored the potential variation in the water chemistry balance difference that could occur between the two.
The water feature is just an independent 2 spouts that bleed off the pump, so running them lowers the efficiency, but it looks pretty.
I'll think about the borates and follow the trend for now. Good info on the aeration effect, thanks.
I definitely see how the cooler nights are reducing cl demand. Between the August heat and the probable algae bloom that was living under my radar, the bleach use was insane. Kids swimsuits faded noticeably.