Overwatering & rot at the base
How to tell
The soil stays wet for days, and the rot starts low: a soft, discolored patch at the base rather than one particular old leaf. 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
Water according to moisture, only when the soil has dried out completely. Check drainage and do not add water just because a tip is brown or a calendar says it is time. Remove rotten roots and repot in free-draining mix. If the base is rotten, healthy stem cuttings with nodes can be rooted warm in lightly moist cactus compost. Keep the rooting mix moist, not wet. Established plants need the mix to dry fully between waterings.



