Water damage spots! How to handle them?

[Bernd]

A new customer has had a water damage on his commercial carpet. There were some spots of the water. A other company cleaned the carpet but the spots come back. They look little brown circles.

He wants me to look for the spots and if there is a possibility to get of the brown circles.

Has anyone a idea how to handle these spots of the water damage? I have read HydrOx could be a possibility...