You should rinse the fermentation vessel thoroughly with hot water before each preparation. If you want to be on the safe side, you can also use vinegar for cleaning.
Be sure to cover the kombucha with a breathable fabric or cloth. This protects it from germs in the air. It also keeps vinegar flies away from your kombucha. This is often the cause of mould on the tea fungus.
To be on the safe side, you can and should boil the tea for a while, contrary to all preparation instructions. This kills off non-cultured germs and bacteria. During fermentation, these could spread and infect the tea fungus. You should also be careful when choosing your tea. Teas with a high content of essential oils, high pesticide content or poor quality can affect the culture. This can then make it more susceptible to mould.
It is very similar with the sugar. It is best to add it to the still hot water immediately after removing the loose tea. Although sugar is a preservative, it does not hurt to be careful and it dissolves better in warm water.
Be sure to add the tea fungus to the cooled, at most lukewarm, tea first. Wash your hands thoroughly beforehand and rinse them well to avoid soap residue.
Beware of recipes that recommend adding fruits or juices during fermentation. These are often carriers of germs. If you want to change the taste of your kombucha, you can do this during the secondary fermentation.
Your preparation liquid should be acidic enough. Also use enough of it. We recommend an amount of 10-20% of the total volume. Many fairmenters let their preparation acidify before they start a new run - even for 10 days.