Aeration/waterfall and ALK question

My pool is 1 year old, pebble finish/gunite pool.

PH 7.4
FC 4.5
CC 0
CYA 40-50
ALK 70
CH 250

My ALK has come down over time. In looking back over my PS-233 kit log it started at 115 and is now down to 70 after about a years time. I have never added baking soda to increase it. I normally have to routinely add acid to lower PH about once a week.

With an ALK of 70 should I look to increase this up to 90 ro so ? Would it help keep my PH more stable ? I wonder if my spa spillover and waterfalls have lowered the ALK over time ? I have a 3-4 foot high waterfall over a grotto, another waterfall in the pool, a spa spill over which runs when the filter runs and a waterfall inside the spa and a slide. Would this provide the areation to lower my ALK over time ?

Normally the spa spill over runs all the time when the filter runs but the others are just on when in use.

thanks,
-- john

If you keep your pH on the low side (7.2 to 7.4 ) then the constant airation over time has probably been lowering your Alk. I would raise it if it were my pool. It might help keep your pH a bit more stable and the ALK and CH work togehter to help protect the plaster. You might want to consider running your pH closer to 7.6 to help minimize the effects of the constant airation on the ALK.