o   If you have just freshly sown seeds in all the sponges and filled approximately 6 liters of water, Herbert should work for approximately 30 days before the water tank is empty.o   The time to refill can reduce itself based on how many plants you have in Herbert and how old they are. If you only have older plants inside that have a lot of foliage, it can also be necessary to refill Herbert every 5 to 7 days. o   You can refill Herbert in any of the slots in the growing module as Herbert is one entire closed water circulation system. We recommend leaving one slot free of plants for refilling and covering the free slot with one of the intransparent caps.