That plant is way over watered. Your medium should not look like coffee grounds. Get a fan pointed towards the medum not the plant, ASAP, to at least get some evaporation going. Since your probalby stuck with that planter water "only" until it dries out, and when you water, use only 2 two cups at the stalk.
A good rule of thumb:
When its cool out, you want wet soil as far as the leaves stretch width wise, anymore and your over watering.
That planter (while it looks cool) is meant for looks on a coffe table in the summer, not growing a healthy plant. Get a cheapo, ugly "normal" planter next time. Ceramic is great for hot weather, but not for the cold. Your mix is not airing out and drowing your plant.