I would treat for cocci.
My birds showed no signs of anything being awry until the morning I opened up their coop and thought a murder had been done in there. Blood everywhere. A quick course of Sulmet and not a problem since.
The problem with letting cocci go too long is that it damages the GI system to the point where even if you cure the problem, the residual damage is so great that birds die from not being able to extract nutrients from the food they eat. So, they eat and eat and eat, but wither up and die from malnutrition because their GI system can't work like it's supposed to. All that blood is coming from the lesions that the cocci has created throughout the GI system.
Good luck with them.