I have these too exactly. I have had them for the past few years, sometimes there is none sometimes there is a ton, I don't know what it is but I think it could be some sort of egg. I believe I have hookworms and liver flukes so far, probably have other types too that I am not aware of. I am about to treat for those worms, hopefully it helps but if the black specs continue to show then I will have to look for other solutions. This is just rough. I hope you find out what is wrong and get better.