Liners are not what they used to be, owners can do what ever they want to a pool..I still believe this is based on antiquated data that the liner companies use. Richard is my go to guy on all things chemical, I trust him over some stupid warranty claim.
Solar blanket warranties are null and void of chlorine levels exceed 3 ppm too
Acid washing a liner is never an option.It will coat the liner with scale. And that is not good as the only way to get it off is acid. And your liner does not like raw acid on it.
Keep your CH within the recommended ranges (under 350 ppm).