My question is in the last paragraph below, but here's some background info:
After nearly two months of being perfectly healthy (getting his appetite back, eradicating worms in the tank, etc.), my 8 year old male RES had some blood drops coming from his mouth last night. I had him dry docked at the time (to absorb some topical skin treatment), and he was doing his usual escape attempts where he tries to climb out and slides back down onto his belly. I was worried that this sliding (which he's done for years without problems), or the q tip I used for the skin treatment, somehow caused the injury, but my vets don't seem to think that's the case. I went to two different emergency vets (because the first was uncomfortable treating turtles beyond a physical exam), and the second one performed x rays and a physical exam; he didn't see any injuries or objects that would cause impaction or injury, and suggested that our regular vet do a fecal sample test and look into the possibility of a bacterial infection or parasites. (He also gave Samuel a dose of Baytril and some fluids). Today, my semi-regular vet gave us two weeks' worth of oral antibiotics, thinking that an infection was the most likely cause (though he has no other symptoms, other than a daily yawn). I dropped off a fecal sample later in the day, so we should get the results of that test in a couple days.
Both vets told me to keep him in his usual tank, but also to keep an eye on him and see if any more blood appears. My question is, how do I watch for blood if he's in his tank? There was blood present for a few hours, but in a tank I feel like it would get dispersed. Should I take him out of the water for a little while each day to see if anything shows up? (He has easy access to an above tank basking area, so I would check him then, but he's never been very keen on basking while there are people around.) I should also note that he is acting perfectly healthy otherwise; he was pretty tired from the trips to the vet, but he has been swimming and eating normally, and didn't even act lethargic at the vet's office.
Thank you for your help!

