I think you are attacking this problem all wrong. Here's my advice.
Salvator are water monitors correct? Lowering the humidity isn't what you want to do, but aiming for ideal husbandry levels is what you want to do. If this normally calls for quite high humidity and you're worried about bacterial growth, then keep the humidity high in addition to increasing the ventilation. Furthermore, a range of humidity can be aquired, (and probably will be should you choose to attempt the aforementioned) with a moderate level cage wide, and higher areas under foliage and in hides.
You may want to adjust the temperature if you feel this guy is fighting infection. Keep the recommended gradiant, but also provide an additional 5-10F on the hot side, and raise the cool side 5F. (80F should be okay for the cool side) This is of course a temporary change.
For medicating this animal your vet may offer injectables, (you'll need a partner to restrain while doing this) or if eating, oral medications can be hidden in food. If you feel that this animal is sick enough to need medications, it should first be seen by a vet where prescriptions can be given as needed.
I don't know your experience, but monitors can sometimes breath hoarse and look "laboured" when pissed off. Perhaps this guy is just not enjoying the handling?
I hope this helps, if I left anything out, just ask 
Ian