I'm not sure this is true. If you shock the pool you would want to uncover the pool at least partially to allow fumes to escape but as far as a solar cover causing a liner to bleach, I'm not sure that is accurate. I add bleach with my solar cover on at times and there are some days that I never remove the cover. When I add bleach (slowly through my skimmer), I always make sure my eyeball is aimed down to send the bleach into the body of the pool water. If my eyeball is aimed up, I think it would cause the bleach to be more concentrated at the top of the water, so I always lower it when adding.