Ask-a-Dave's-Gardener: Household plants dying, 4 by travikk

travikk wrote:
Hey, so I\'ve been having my plants for some time now and every now and then a leaf dies, so i cut it off and a new pops up. They always go the same way - white spots all around and eventually the leaf turns brown and dies. It happens on a few plants around the house so finally I thought let me do something about it.

Here\'s a sample of what it looks like on two different plants. What is it and what can I do about it to cure my babies?