93/f. Watery black Dirreah can't get it to slow down or stop. Tried A/D meds. Recently on Iron rx. What is Goin on?

Quite worrisome. As 93 years don't tend to do well with any significant diarrhea. They are much more susceptible to dehydration and its complications compared to someone younger. Also the blackness may be related to the iron use but could also be related to bleeding. Consider being evaluated in person and soon to make sure nothing more concerning isn't going on.