Thank you everyone for your thoughts so far. So I have three different pothoses, and it was suspicious to me that all three of them started developing black spots around the same time. I almost wonder if there was a bacterial infection in one which spread to the others? I have had the plants for over a year. This past September they were all left at different friend's houses for a week while I was on vacation. One of them might have picked something up while they were there. They were all fine before that.
As requested, below are better pictures of each of them.
Pothos 1 (this one looks the worst, and has been black the longest):
Pothos 2: this one I made the mistake of giving some plant food to about a month ago. I thought it was malnourished. Then some of the leaves started turning yellow and falling off. It has not done this as much recently. However, it does have some leaves with black spots as well
Pothos 3: this one looks the least bad, but is also developing black spots on new and existing leaves
