Answer: For good germination it's important to keep the potting soil moist, but it's also important to allow for good air circulation. I think the conditions are overly moist, or there's a lack of air flow around the plants. Try watering from the bottom rather than the top so water is wicked up through the soil rather than travelling downward. This will keep the topmost soil slightly drier. Place a fan in the room to circulate air and help dry out the tops of the pots. If the mold is white, it causes more concern than if it's a green algae bloom. You can leave it alone if it's green. If it's white, gently scrape it off the top of the soil before it compromises the health of your seedlings. Once you've corrected the air exchange and soil moisture, everything should be just fine.
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