It seems there are way more things that can go wrong with a plant than I realized. It’s not always as simple as pinpointing under watering, over watering, or lack of sunshine. Specific nutrient deficiencies can be the culprit to your yellowing or dropping leaves. And there are several nutrient deficiencies with varying remedies that can be employed!
The image above is a good reference, but be sure to read the article below which gives even more information of what might go wrong with the plants in your life!