we have an in-ground jacuzzi 5,000 gallons that has a waterfall. a couple weeks ago we scrubbed the tiles with a pumice stone and it looked great. now the stain is back, it is sort of a brownish color around the tiles. we use 3" chlorine tabs for sanitizing. could the waterfall have an effect? the ph stays at a constant 7.2-7.8. i am baffled as to what it could be and how to prevent it and any help would be great, thanks.