yellowing on bottom leaf but rest are fine?

That is normal. Check out my diary with C99, and you see that I have had yellowing leaves through out my grow and at different levels of the plants. They look great going into flower. As long as the new leaves are the deep green you are looking for, and they stay green for a while, then there should be no problem. Good growing.

There's nothing to worry about. It's normal for the cotyledons to yellow and fall off. They store food for the roots during the seedling stage so that they can develop enough to start getting nutrients from the soil. Hopefully, I answered your question and remember " Happy Growing and Free your mind one puff at a time ".