Some one may kick my arse for saying this but I never had respiratory issues when I had leos in a 40-50-ish humidity climate or so.
Climbing 60 , well...
Short of getting a dehumidifier, the only things that keep humidity down are good ventilation, heat, and substrate that won't retain moisture. Air flow helps a ton, but drafts are a definite N-O. You can't really increase heat but I swear that overhead lighting (while not preferred) reduces humidity slightly more effectively than UTH or flexwatt heat. And substrate options are limited - just get them off bed-a-beast and anything else fiberous if they're not on paper towels. Not too much you can do apart from getting a dehumidifier.
What type of gage are you using to measure the humidity and where is it? (ie, the weather channel website listings for your area (hehe), a cheap-o stick on hydrogemeter, a slightly more effective/expensive option?)
And do you have access to air conditioning? A/C does the trick.
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Too many Leos
1.0 feline "Spot"
0.1 canine "Tika"