This succulent's leaves are turning brown toward the center of the plant (unfortunately it's hard to see in the pictures). It is out on my porch where it gets a lot of indirect sunlight. I try to water it whenever the soil gets dry, but it is only in regular garden soil, so it may still be getting too much water. I have a few other plants in this same pot, and they all seem to be doing fine. Any help would be greatly appreciated!