Our pool was built in 2007- 17 years old. The liner has a 20 year warranty but it has faded a fair amount below the water line (probably due to over-chlorination a few times) and is showing some mild brown staining above the water line (reasons unknown, various remediation attempts had little impact). Despite the warranty, I'm concerned that the liner is closer to it's end-of-life than the warranty implies. It is an IG, outdoor pool in Minnesota but we have an autocover and it is closed at all times except when we are swimming so UV damage should be minimal. I'm looking for guidance on what is a typical longevity expectation for liners in an environment like ours.