Answer: Based on your description, it is possible the plant needs to be repotted again or, if it seems very dense and crowded, it may need to be divided. The plants will grow slower when very crowded, and tend to lose vigor as they age and so division will rejuvenate them.
If it seems alright as far as the potting goes, then it is also possible that a little more bright but still indirect light would be helpful. Increase the light gradually so as not to shock the plant, and avoid direct sun.
Also take care to keep the potting soil moist, as a plant grows larger it tends to absorb additional moisture from the soil in proportion to its size. Depending on the ambient humidity and temperature you may need to water more than once a week.
Next, this plant is sensitive to mineral build up in the soil, so you might want to flush it several times with water to leach any possible build up from fertilizers. Then use a water soluble fertilizer labeled for foliage plants and do not exceed the amounts recommended on the label. You may want to fertilize more often in the spring and summer when the plant is actively growing.
One additional suggestion is to treat it to a humidity tray, meaning a tray filled with pebbles. Set the pot on the pebble layer and add water to the tray to just below the bottom of the pot. (Do not allow the pot to sit in the water.) This works well to humidify the immediate area.
Good luck with your plant!
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