Rot from the bottom up is usually a sign of inadequate drainage or too much moisture.

The yellowing of the leaves is a general sign of stress, in my experience, and may be caused by just about any condition that the cutting doesn't like. It could be the moisture level, but it could also be excessive heat or a less than hospitable pH. Or it could be that the cuttings were either taken from a thirsty plant or weren't kept sufficiently hydrated during handling before they went into the aquarium.

I find yellowing leave most common when they are overwatered. I put my cuttings in the coir that has been well watered, cover with a plastic bag, and LEAVE THEM ALONE and don't love them to death. That is what my problem used to be. I just always was taking the cover off and fussing with them and watering them, etc....just loved them to death. Now I just plain ignore them for 8 full weeks after sticking them and my success is much improved. Also, I don't put rooting hormone on the tip of the cutting. I only put it lightly on the sides where I have lightly skinned the cane. I think the cane takes up moisture better this way and this has improved my success as well.
John