As long as it's not yellowed or mucousy, it's normal - happens all the time. It's just the body ridding itself of excess salts, like you thought. I wouldn't worry about it. The humidity is fine, too.
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Torey
Eugene, Oregon, USA
1.1 Saharan Uros (Joe and Arthur)
3.0 Mali Uros (Spike, Turtle, and Tank)
1.1 Ornate Uros (Scuttlebutt and Shazzbot)
1.1 Collared Lizard (Ripcord and Rorschach)
2.0 Green Anoles (Bowser and Sprocket)
1.1 Chubby Housecats (Roscolux and Jenny)