Eucalyptus oil has high levels of the same type of aromatic phenols that make even just cedar wood a dangerous choice for reptiles. It's not really a safe choice in any amount :/ Eucalyptus oil likely has at least some efficacy against microorganisms, but that same mechanism will irritate the lungs and damage the liver and kidneys. One of the biggest challenges in medicine is to get something that is targeted to the undesired organism rather than just something that is efficacious against the undesired organism but also does damage to the host. Please at least consider the potential side effects of using eucalyptus oil that can't be readily seen.