Scarlet Crystal is an ingredient required to make the only medicine that can treat the Iskan Fever. The treament is just for subduing the symptoms and is not a cure. The amount of this ingredient needed to make the medicine seems to be proportional to size of the individual that needs to take it. In the case of Maya, only a small amount of the crystals were needed compared to the average adult.
The main source of Scarlet Crystals is heavily controlled by Zanzibar who holds a monopoly in the supply which he sells expensively. Doctor Daleyon somehow knew that there were some Scarlet Crystals left in the Altago Old Waterways.