I have an in-ground, concrete, saltwater pool that is approx. 18 months old. The stainless steel hand rail turned dark gray/black from the waterline to the bottom of the pool. All chems. are perfect. Handrail was replaced by pool builder and turned blk. within two weeks. No one knows why or have ever heard of this problem. Any help resolving this issue will be greatly appreciated. This problem just occurred about two months ago.