This reminds me of a project we did a few years ago. It turned out that the culprit was a water softener. The yellow residue came off easily and it wasn't really staining per se.  Once they shut down the water softener the problem never came back. It was only in the grout lines and not in the marble. Ours was also a new installation, so my guess was that something in the water softener was reacting with some additive in the grout.  Ask if there is a water softener. 
B

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On Tue, Oct 6, 2015 at 3:06 PM, Stuart Young <santafefc@sbcglobal.net> wrote:

This is a new installation.  The darker areas are turning yellow.  Makes me think iron.  What can be done?  Tests for iron?

Thanks in advance 

Stuart
Santa Fe loor Care
Begin forwarded message:

From: Stuart Young <santafefc@sbcglobal.net>
Date: October 6, 2015 at 1:59:19 PM CDT



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