We recently purchased a Jacuzzi brand spa and are having problems with some brown scum that appeard right after the initial startup. I have cleaned the scum at the waterline several times and also cleaned the net, but this stuff keeps building up. The bottle of the "Stain & Scale" stuff seems to have some kind of long strip of brown gunk in it. Do these chemicals have a shelf life? I should mention that the dealer set this spa up in the dark. We didn't look in the bottles before we used them.