I am about 38 days into flowering and a few of my fan leaves on the bottom have fallen off and alot of my leaves in general are becoming yellow, while most of the ones at the top are still green. I have about 22 more days left of flowering.. is it normal for leaves to start dying around the 30-40 day mark? I don't want my leaves to be all gone when I need them the most ( last 2 weeks)