A few things:
Are they all still growing leaves?
If it's one of the cooler seasons where you are, pings are going to start growing smaller leaves that are more tucked into the plant. During this time you should hold off on watering. Let the substrate the pot get a little more on the drier side before you water again.
If you can, peek at the area where the leaves originate. If it's brown, well, my condolences. It's browning heart. If it's not brown or browning, you should be okay. I don't know where you grow these plants, but make sure there's some degree of airflow. There doesn't have to be a fan blowing on the plants, but the air can't be stagnate.
While it's not a huge deal, the plants look covered in the substrate. Most pings just need to have their roots in a smidge in the substrate. In nature Mexican/Tropical pings are lithophytes; plants that grow in or on rocks. They're roots just grip onto the top of the rock(s) or in any cracks in the rock(s).
Here's a few articles/videos from the people at Curious Plant that could be useful: