Rephrased, your soil has too many fine particles to allow it to hold enough air, and the fine worm castings make the problem worse. Your plant is dying of thirst in a sea of plenty because of impaired root function, while the roots are also likely rotting due to the anaerobic (airless) fungi multiplying in the root zone. It's a very common issue I've seen hundreds of times. The soil is the foundation of every container planting. You can try to build on a weak foundation, but you'll be fighting against the soil for the entire life of the planting.
I'm not trying to be critical of you or trying to take a lofty perch so I can look down. I'd be very happy to help you fully understand what I'm saying if you're interested in learning. I've helped (literally) thousands of people in your exact predicament turn their growing experience into something more rewarding by instilling a better understanding of what differentiates a good medium from a not so good one or a poor one.
To illustrate, I grow in only highly aerated soils, use commonly found soluble fertilizers, have almost no worries about over-watering - ever ...... even during extended periods of rain when my plants are outdoors, and consistently produce extremely healthy plants with very attractive foliage ....... and it's easy because the soil is working FOR me instead of against me. See picture below.
Plants are genetically programmed with a certain amount of vigor (something almost everyone mistakes for vitality). Our job, especially as container gardeners, is to eliminate those things that limit the plants ability to grow to its genetic potential. The big 3, in order of their significance insofar as your success is concerned are soil choice, watering habits, and light. Of course there are other considerations, but easily 80% and perhaps 90% or more of the issues discussed as 'problems' on these (container gardening related) forums can be traced to the first two mentioned - soil choice and watering habits.
Al
