I too have the heating/ac issues and I've found that coconut bark chips hold the humidity quite nicely. Coconut earth also holds the humidity, but not as well as the bark chips. T-rex makes it.
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Lisa
1.0.0 P.m. grandis (Linus)
3.3.0 P. standingi (Kona and her 5 babies)
R.I.P. Toby (7/5/06) I miss you...

