Alright, so I went to my local 'growing' store and was talked into getting a 'living soil' that contained all the nutrients the plant needed.
The plant has been moved outside since it's the first time the warmth could be relied upon. Plant was transplanted into a 19 gallon pot (recommend by the sales clerk), which I later realized was unnecessary.
I knew at this point that the yellowing of the leaves was a result of a nitrogen deficiency.
I also choose to spray the leaves with Safer's Sulphur Dust Fungicide and Miticide. I used 15ml/l and sprayed it over and under the leaves. It left a powdery mildew, so I'll be using Neem oil in the future.