About the subtrate

Maybe it's just my QT room, but it seems to me like bloods (in my case, Borneos) have a bit of an odor that balls don't.

What are you keeping them on? They do pass a lot more liquid waste than balls and much more often so if they are kept on cypress or something similar, it might soak right in and go unnoticed except for the smell. I keep mine on paper and they don't normally smell, except when they go - then it's really bad. At least it's really easy to tell when the cage needs cleaning. :D
Mine will often pass waste in their soaking dishes anyway and keep the paper pretty clean.

That's what I thought at first, but I've checked the enclosure over and over again. Can't find anything. Maybe it's the quarantine room.