Mouldy cistern

[Moon~Shadow]

I'm hoping someone may help. The inside of our toilet cistern including the fittings are covered in black mould, there is even a line around the water rim. I have used bleach in the past to clean it but cannot work out what is causing it, there is no damp in the bathroom and plenty of ventilation. The cistern is a porcelin type/ceramic inside and I never had this problem with my last one. This one has only been fitted 3 years - would replacing the plastic fittings inside with better quality ones help? Any advice, most appreciated.

[Andrew Gabriel]

Bleach is not a cleaner, it just makes the dirt colourless so you can't see it. You could try using a proper cleaner and brush to remove whatever the mould is growing on.

Where does the water supply come from? I'm wondering if it's contaminated with some organic matter. If it comes from a loft tank, you might want to check that's clean.