>>The tank is pretty dry even though I spray so often... I live in the Southern California desert and it's very hard to retain humidity.

are you using a hygrometer to measure it or just guessing? shed problems can also be caused by TOO much humidity. the skin needs to be a little dry to peel off, or it will just stick on the gecko.
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4.1 snakes, 4.6.1 crested geckos, 0.1 gargoyle gecko, 0.0.2 red-eyed tree frogs, 2.0 devon rex cats, 1.0 betta, 0.1 sun conure, 1.0 lovebird