We use dry kibble only. Water dish at each end of the tank is always full. Mist the racks once or twice a week. No substrate. The tank is kept dry to avoid molds and volunteer flies.Really? This for the dry kibble or is it the semi-moist chews? Are you misting the enclosure or does it have high humidity? I tend to avoid the mold and other flying pests by keeping the enclosure dry, providing only light, occasional, fine misting and using moisture locked foods like the Bok Choy or the occassional overnight grape or small tomato that I can easily remove the next morning.
I also mist away from the food which i cover with the egg crate so the dry stays mainly dry. Its funny to see the whole colony empty out of hiding from within the egg crate and flow like a brown wave of destruction to drink when I mist the wall. It may a bit dry for them sometimes, but they're roaches, they'll be ok.