We habe a liner pool. It is 4 ft deep, will the bleach the liner?

Most shock/ chlorine are safe for the liners ; I bought it once- it's over priced and wasn't a fan ! I use hth shock and I usually just buy it at Walmart works the best I think ! - you are paying for the name Clorox ! It's concentrated bleach pretty much a no brainer -hope this helped you . Enjoy your summer my pool is already open! 😬

How many gallons of water is each bottle supposed to treat?

To shock, one bottle does 12,000 gallons.

Does this contain cynauric acid ?

Cyanuric acid isn't listed as one of the ingredients and I've never had a problem with rising levels of acid. Just make sure you mix it with a bucket of water and pour it in as you're walking around the pool. I use it mainly to close and open the pool but I do throw a bag in from time to time just to boost the chlorine level in my pool.