EPDM pond liners are much more flexible and resistant to damage than PVC, and will last for many more years. PVC has developed a questionable reputation over the years because plasticizers like phthalates are added during manufacture to help PVC maintain flexibility.
Unfortunately, these plasticizers have been found to leach into the water over time, which could potentially affect the health of your fish. PVC is also very vulnerable to UV and ozone exposure, causing it to yellow and become brittle. When your PVC liner reaches this point, it requires total replacement.
