I purchased a Pentair Salt System in October 2007 when I had a new pool installed. The Pentair was installed by a professional. In September 2008 I began having a problem with my pool tile being stained with black. I contacted Pentair who told me they never heard of such a thing. My pool has always been maintained by professionals. After much research and cleaning, in November of 2008 my pool looked like new. In September 2009 the black stain came back. I again contacted Pentair who offered absolutely no solution to this problem. They refused to come and look at the unit. I finally hired an independent contractor to inspect the unit and he advised me that the ruthenium on the fins has dissolved. This unit is still under warranty. Pentair has offered no help at all. After I contacted the Better Business Bureau, they responded with some nonsense about underground wires which we do not have. This stain can only be removed with M. Acid. It cannot be scraped off for analysis. I have city water.