i keeping my dubias colony just as you, in primitive set up lol.
for diet i mainly use veggie chow, fruits, and pellets and watering via water crystals. That work just fine
i stacked my egg flats vertical so dubias waste can fall easily to bottom of the tub, nymph will use adults waste as their food.
i keep my male to female ratio in 1 : 3 . So i think you need extra males, but no worries you can keep it as it is and keep more male in next generations.
for heating, i dont use any heat source hence i live in Indonesia. Its pretty warm here, around 84 - 86
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