Oh man, I got reprimanded by soil growers in here for giving advice on soil while I only grow hydroponics
![Hit Wall :wall: :wall:](/styles/smilies/wall.gif)
and yes, they have a point.
I don't know about Miracle Gro soil and their slow release of nutrients (or as someone in here said, they release nutrients when you add water).
All I can do is share an old grow photo of mine having these symptoms but they were more severe and for me, it turned out to be a nutes deficiency. It started with one lower leaf, then the second one and it just kept progressing. Here's is the photo (note this plant looks strange because I topped it very early):
View attachment 4550446
It may be a PH issue for you that's locking out some element uptake.