-- you can leave the CH @ 70; CH is NOT an issue in vinyl pool (contrary to all the pool stores, who want to sell you some) UNLESS the CH is too HIGH.

-- add tabs to add chlorine, not CYA. BUT, monitor your CYA level, so you can stop using tabs before it gets too high.

-- Pool numbers are not a target; rather, nice safe clear pool water is the target! To achieve that, there is an acceptable RANGE of numbers, and if you are in the range, you should NOT try to hit a 'target'. Over-treating and over-adjusting pool water is a common, common cause of pool water troubles.