I believe you have root rot. Go look at my Gorilla diary for similarities. Start by keeping the drip trays empty (after you water drain them). Second I suspect you’re water to often, although if you were not emptying the drip trays this may not be true as that would explain why the soil looks so moist. To determine proper watering we should wait until either the medium is dry for the top 1/2” or when the soil loses about half the weight (yes you can weigh them if you want a comparison for the other method or just so you get a feel for what the soil feels like when it’s time to water.
Third like Ripper said cut back on the nutrients (high nutrient levels also contribute to root rot).
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