Calatheas are notorious for needing high ambient humidity in order to be happy. Anything below 60-70% and they start whining. Curled leaves, crusty brown tips and/or edges... ugliness everywhere. You might be tempted to water them more, but if your plant was doing fine then you risk overwatering it, which is generally much more dangerous.
The most common way of increasing air humidity for plants is, either surround it with more plants, or place a pebble tray with water not in direct contact but near the plant. Many houseplants including Calatheas also like frequent misting, especially when it's hot.
Aside from that, maybe you could try giving it less water but more often, so that the soil doesn't get too dry. The temperature is a bit on the lower side too, your plant would like it better at 21-24C (70-75F). Also, be wary of air currents near doors and windows. Your pictures don't look like an infestation, but check the back of the leaves for spider mites and the like just to be sure.
Keep in mind that a well-established Calathea, which is happy with its soil, watering, temperature and everything but air humidity, can be growing vigorously and showing dry leaves at the same time. I had one for 5+ years, and almost every week I had to trim at least half a dozen ugly leaves (not the best climate, too dry), but the thing never seemed to run out of new ones.
