The leaves of my African violets are falling off otherwise healthy plants. It starts with the leaf stem turning almost clear and a few days later the leaves fall off.
Cold water or salt build up can cause this type of damage. Use room temperature water to avoid cold damage to the above ground growth. Then check for salt build up, a white crusty substance on the soil surface or plant container? The salts are from the minerals in the water and fertilizer. African violet leaves and petioles (leaf stems) are damaged and often drop when they come in contact with this material. Most African violet growers raise their plants in plastic or ceramic pots, with drainage holes, to avoid this problem. Start by scraping off the crusty white substance. Then water the soil thoroughly with room temperature water. Allow the excess water to drain from the pot. Repeat this several times at 20 minute intervals. Leaching the soil like this will help wash any excess salts out of the soil. Some growers cover the rim of the pot with foil or a similar material to protect the petioles from the salt laden container rim.