Burnt leaf tips are often an indication of a watering issue, either over or under watering. Use a wooden dowel or probe to get down at least 4 inches, if it comes away damp or dirt clumps on it, then too much water.

A close up picture of the white spots would help.

I would check in the houseplant forum for ideas. One possibility is that I'd you haven't changed out the potting soil and you've had the plants for at least a year or more, they may need new soil. Most potting soils break down over time and loose the spaces that allow air in the mix, leading to unhealthy roots.