Check each rat all over for any cuts or scrapes. Often small cuts will bleed quite a bit, though rats heal well on their own. If you do not find any cuts or scrapes at all, then check around their nose and eye area for signs of red fluid. This is called porphyrin, and it is often mistaken for blood, but it is actually the color of their mucus. Sometimes you will see it on their blankets, particularly in their sleeping area, because it is common for them to have a bit accumulate while they sleep, but they normally wash it off right after waking up.
So, first check for cuts, scrapes or other injuries--check all over each rat carefully. You might also look at their toenails, since it's possible that one got caught on something and is bleeding a bit. (This is fairly common.) Next, look at their eyes and noses for signs of porphyrin staining. If you don't see any of those signs, keep an eye on them and see if it continues, and try to figure out who it is.
If there's blood in his urine he likely has a UTI (urinary tract infection), which can be fixed up relatively easy with antibiotics. This is the most likely diagnosis, but there are others...internal injury is another one.
Update: He started getting better on his own but we took him to the vet anyway. On the way to the vet he started to leak red out of his eyes.. it was porphyrin and i am guessing that was in his oee too. By the time he went to the vet he was peeing normal. The vet did find some kinda lump in his belly tho.. so we have to watch that. He is back to his normal self now terrizing the rats above his cage!!!! LOL
sometimes my males do that when they breed,, sometimes they dont know when to stop and end up bleeding,, if he is a dominant one he may have irritated the area,, uh yea kinda hard to explain,, feel free to message me
I am also wondering about the lump. When one of my ladies started urinating blood I rushed her to the emergency vet to find she had tumors inside and would eventually bleed herself out since her pee was primarily red blood cells, I had to have her euthanized. Be careful!