I have measured accurate pH with chlorine levels higher than 10 with a very similar kit to yours (that uses Taylor reagents), so I think that you're probably getting an accurate pH reading with your chlorine at 10. As far as how quickly aeration raises pH, that depends on the pool and the amount of aeration (and some on the level of TA itself). A waterfall would definitely raise pH by aeration quicker than a return pointed upward. I find that a pool full of 10-year-olds raises it rather quickly!

Janet