Help with Janet Craig

Hi- I was wondering if anyone could help me with my Janet Craig plant. I bought the plant a month ago from a nursery. I went to them for help but they weren’t sure the exact issue. The plant is potted in lava rock (no potting soil added). This is how the nursery maintains the plants. It gets low to medium indirect light. I watered the plant when I got it. I waited 10 days to water it again. I then started to get yellow leaves and other yellow with black spots. I wondered if it was too dry so I watered it after 7 days the next time. The yellowing continues up the black (starting at the bottom moving up the plant). The temperature in my home is normal with normal humidity. There are no drafts near the plant. I use touch and a moisture meter but the lava rocks are very difficult to judge when they are dry. My concern is the amount of yellowing (I’ve already taken a lot off) and the black spots that also are on some leaves and at the base of the leaves near the steams. I only use filtered water and did treat it with neem just in case it was a fungus. Thanks for taking the time to help!