Ant excreta, prey remains, etc. will cause moldy nests, which is unavoidable in the process of keeping ants. However, do not worry, as healthy ants will disinfect their nests and clean themselves properly, so moldy nests will not have any negative impact on healthy ants.
We can inhibit or minimize the moldy condition by lowering the amount of water added to the nest, letting it dry out a bit, cleaning the feeding area and avoiding feeding live animals.