Humidity rises during the dark cycle

My humidity is in the normal range when the lights r on,but a few hours after the lights go out & the temp drops to 64-65 degrees the RH is about 75%.It seems high to me,Is it?? will it cause problems to my girls eventhough im not in the flowering cycle.How about when i flower??Could this cause powerdy mildew???Will a circulating fan help?
My room is small 3.5x4.5 and wall to wall plants.No foom for a dehumidifer.any suggestions are helpful.Thanx

Maybe something like this: http://www.amazon.com/William-Barr-...?ie=UTF8&s=home-garden&qid=1261438303&sr=8-12

And this seems pretty small and is wireless: http://www.amazon.com/Eva-dry-EDV-E...=sr_1_15?ie=UTF8&s=hpc&qid=1261438303&sr=8-15

Flowering is best in low humidity, 35% or lower is recommended. Yes, high humidity can certainly cause mold. A circulating fan or two will help with many things as plants need to breath. Not sure if a fan helps with mold specifically.

they make dehumidifiers for closets that are pretty small i would make room for one

As temperature drops, RH naturally raises, you will
need to control this, otherwise you will probably
begin experience issues with powdery mildew, and other
fungi/molds, either a space heater to keep the temp at 68-70
in the off cycle, or a dehumidifier.