Quote Originally Posted by CarlD View Post

But too-low calcium is NOT an issue for vinyl. And when it's low, higher T/A levels are fine.
One often overlooked reason for having calcium in a vinyl pool is to help prevent foaming. Soft water will have more of a tendency to foam than hard water. Personally, I think a calcium hardness of around 100-150 ppm would be more than enough. Might be in intersting experiment if anyone cares to do it! Other than that low calcium should not be an issue at all!