Brought my 7 foot FLF home 4 weeks ago.  Watered 1st time until water appeared in the saucer, then used a turkey baster to remove all standing water.  Now water weekly with 4 cups of water when the top soil is dry down 2 inches.  Planted in a 13 inch plastic growers pot in very loose soil.  The tree is about 10 feet opposite a southern window.  Good indirect sunlight.  Am losing 2 to 3 leaves a week.  The leaf starts to turn grey in the center-then falls off.  Also there are brown spots in the middle of a leaf and at the tip.  Seems the very lowest and very highest leaves remain healthy, in between is where I’m losing the leaves.  What is going on?  Help please, and thank you!