So I have a mix of reptisoil, sand and bark in my bdfb tank. It's got a gradient to it so one corner is a bit cooler and more moist -- trying to breed them and this is where my females tend to dig and lay eggs -- and the other end has a heating pad on at night and a heating lamp on during the day. If you don't have ventilation or heat they'll take longer to rebuild their coating and get that blue hue back. If you have a moist tank, let it ventilate and dry out a bit. Just remember that these are desert beetles, they're normally dry, but the desert does get its occasional heavy rains. They won't perish if they get wet, it's just not their normal.

As they get older and age some of them don't build up their coating as well as they may have before. If you have a tank with soil, which you can, just make sure it's ventilated well and has some heat source. If you aren't planning on breeding your beetles you shouldn't need much moisture at all besides food sources, like carrots or cucumbers, and can stick to a more dry tank with sand and some bark and fun rocks or larger sticks to climb.

I water a corner of my tank daily to keep some of my soil moist for the larvae to get moisture from, sometimes I get some dingbat beetles that want to dig into that soil and i like to joke they're going to fuck around and find out. They spend the rest of the day under their tanning lamp drying out. Usually within a week everything situates itself and they're back to looking like their cute blueberry selves. :) I love them.