Hi, I keep getting a build up of a black algae type growth on anything connected to my cold water tank. It doesn't happen in the kitchen tap but the bathroom sink coldwater tap, bath tap and shower head (electric mixer type) all show this growth. Can anyone advise what it is and how to stop it happening. I have had a look at the tank in the loft but it seems pretty well sealed with insulation and I was loath to take it off. The house is approx 15 years old. Thanks, Richard