Depending on what exactly is going on, you may just be mistaking a normal, but yucky, bowel movement that is made of a sticky stinky dark or medium brown fluid called "cecal fluid." Keep an eye on them- if they are all doing this once every 5th or so poo, it is normal and healthy. It is part of their digestive process.
I thought it was diarrhea at first too, but then I read a bunch on this forum and discovered that it is just part of their waste removal cycle.
Now, if a single chick is doing this all the time, that is different.
-MTchick
