Wicks are green or brown

It may not look nice, but it is normal.
The capillary thread acts as a "channel" through which the water flows.
Over time, minerals and nutrients present in the water build up in the thread. When reusing wicks, wash them out thoroughly.

So as a rule it is not mould or anything similar. We recommend replacing the threads with new ones once a quarter.
You'll find new threads as accessories via the urbanhive app or in our online shop.