HoneyBunny31
Doesn't look like root rot. Does the soil smell like soil or a leaky sewer pipe? Is the soil soaking wet all the way through or, if you dig your fingers deep into the root ball, is it dry in the center but damp on the outside? (don't be afraid to do that). Has your weather been really hot for the past few weeks? Have you fertilized it, if so with what and how often? I suspect your calibrachoa just needs a good soak, a little fertilizer and a mid-summer haircut, but answer the questions and we'll know for sure. Also, close-up photos of the foliage--brown and green--would be helpful.
