Bob Staebell is the right person to ask, but I'd say 30 days seems short if he told you 90 days.
When you clean the unit, are you flushing everything with distilled water and then drying with a very clean, white, lint-free cloth?
It may help to know which wick. Here is the link to the wick order page:
http://www.aristocrathumidors.com/wickorders.htm