Dark Oily Coating On Spa Surface
A black, blue, or green coating on the spa surface is high copper. This usually happens if the ECOsmarte box is on left on "ionize" rather than switched over to "oxidize". It causes no harm to the spa or bathers and is removed with a cloth. The copper needs to be removed from the surface to get the copper level back down to .3 ppm - .7 ppm. This might best be done by draining the spa, wiping down the surface, and refilling. The spa filter also will need to be cleaned.