My ponytail palms have developed white specks on the leaves. Also, the tips of some of the leaves have turned brown. I am very careful not to water too much. Thanks for your help. I have them inside with indirect lighting.
Brown tips are almost always the sign of soil that is staying too wet, also known as overwatering. The question to ask is not how often to water, but how to know when to water. The answer is water when the soil in the bottom of the pot is almost dry (completely dry if the plant is in lower light.) In order to find out how much moisture is in the pot, you need to test the soil. You can use a thin wooden dowel or bamboo kebob skewer as a tester, pulling it up and running it between your fingers to feel for soil dampness. Or you can use an electronic moisture meter: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm