In the case of tempeh keeping the right ambient temperature (~30) and adding a bit of vinegar to the beans is the best way I have experienced to make it grow fast and healthy. The CO2 I only measure to check for stale air. The tempeh fungus breathes in oxygen and exhales CO2, and if you have a lot of tempeh in a small incubator the CO2 can get too high.

In some techniques for mushroom growing, the mycelium is grown inside of a tub. The fungus exhales CO2 into the closed tub and inhibits this high CO2 condition inhibits fruiting. The fruiting stage can be stimulated by using a fan to push out the CO2. In the case of tempeh one can surround the tempeh with fresh air to stimulate the tempeh to produce spores, which can then be ground with white rice to create a powder to inoculate a lot more tempeh.