I removed the plastic domes from the flats with taller seedlings, as I've read to do. But I see that 1 flat has what appears to be MOLD on top of the soil in each cell, some touching the stems… WHY IS THIS, & WHAT SHOULD I DO?!? (they SHOULD have plenty of circulation…??) Now I'm nervous about the rest of them; it's still several weeks til planting time—HOW SHOULD I CARE FOR THE SEEDLINGS ONCE THE DOMES COME OFF?!?