The white build up is like mealybugs, a crawling sucking insect. They are difficult to get rid of and you'll want to consider whether the risk to other plants in your house. Pictures and management options for mealy bugs can be found here: https://extension.umn.edu/product-and-houseplant-pests/insects-indoor-plants

Houseplants are most likely killed because of too much water. According to the webpage on the Y. elephantipes from the Missouri Botanical Garden, this plant prefers to dry out between waterings and requires minimal watering in winter, likely because it's not growing very much. So rather than follow a schedule, feel the soil before watering and water only when the top few inches of soil plant are dry. 

Make sure the plant is growing in a pot that drains well too. Continuously wet soil rots the plant roots, ultimately killing the plant. If your plant sits in a decorative pot to hide the black nursery pot (called double-potted), then be sure to remove the plant (in the nursery pot) from the decorative pot each time to water so it drains well. Then return it to the decorative pot. 

If the water doesn't seem to soak into the plant soil but pours out from the holes in the pot, the plant is likely pot bound - a case where the the plant roots circle the pot and are so dense that there is really very little soil left in the pot. Some houseplants have outgrown their pots by the the time we bring them home. So repotting is necessary. Use an all purpose potting soil for indoor plants from your local garden center and re-pot into a slightly larger pot about 2-4" wider in diameter.

If the soil is drying out sufficiently between waterings, then consider the amount of light the plant receives. It may need more. If this plant doesn't work out, check our lists of plants for low, medium and bright light on our webpage Light Requirements for Houseplants.