There's no need that I know of the keep a constant 70% nor going up to 90%. You'll be fine if you can get it up to 50-60% until shed in which you'd want to get it up to 70%. If you're having a hard time keeping it at 50, a good tip is to put tin foil on the top of your tank assuming you're using a mesh top, and cut holes for airflow as well as for any heat lamps you may have. As soon as I did that, my levels for humidity were great.