Answer: The most common reason for this is overfertilizing. The fertilizer salts build up in the soil over time. To correct this, water the plant heavily and allow it to drain, then repeat several times in succession. This should leach the soil.
This plant needs only a light fertilization program, so use the lower label rate from spring to fall. Do not feed in the winter months, or feed half the lower rate only once a month during winter.
Another possible cause is fluoride in the water. At some rates, it can cause leaf tip discoloring on the older leaves. You could try watering with rain water or with bottled drinking water (not distilled water).
Another possible cause is lack of humidity, but you would usually see this in midwinter when the heating system is turned on and the indoor air is very dry. To combat that, use a humdifier or set the pot on a pebble and water tray. This is a shallow pan filled with pebbles, set the pot on the pebbles, add water to the tray so it is just below the top of the pebbles. (The pot should not touch the water.) Replenish the water as needed due to evaporation.
Also make sure your plant is not in a draft, either hot or cold.
I hope this helps.
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