Overwatering & early root rot
How to tell
The soil is still wet days after watering, the lower and oldest leaves yellow first, and the stem base may feel soft. Small dark flies around moist potting medium may be fungus gnats. They suggest conditions suitable for breeding, without proving that the surface never dries.
The fix
Stop watering. Make sure the pot can actually drain, and wait until the top 3 cm (1.2 in) of soil feel dry. If the base is mushy or smells sour, unpot it and trim any brown, soft roots before repotting in fresh mix. Wear gloves before cutting or dividing. Sap or foliage can irritate skin. Avoid contact with eyes and mouth, and wash your hands after handling. Keep cut pieces out of reach of children and pets.
