I use bioactive substrate and only bioactive substrate. Its the best way to go If you are using lots of soil for an animal or making a nice viv that you don't want to destroy everytime you cleen the enclosure. Bio-active substrate is the soils natural bacteria that breaks down waste matter and mold. For frogs I prefer to use bioactive soil and for reptiles I use bioactive sand/soil. A good way to introduce helpful bacteria into your enclosures is go out side and pick up leaf litter.