Q: My Tortoise has a nasal discharge he is on antibiotics but it does not resolve. I am using Baytril at 22.7 mg/ml
A: What were the dosages you or the vet administered to the animal?
You have given the concentration of the drug in solution but not the dose rate.
Do not let the temperatures drop at night, keep the animal around 86 degrees they need their metabolism up or they can't even metabolize the drugs you are giving them.
Your culture reports don't show signs of anything pathogenic, but keep in mind these reports are not very diagnostic for two reasons
#1 you don't always get the germ in the discharge and
#2 you always have so much contamination you're not really sure what you are culturing in the first place.
Now I can't give you medical advice and I think you should go to a competent Tortoise vet but we had a very similar situation and what I did was Inject with Baytril 5mg/kg im and then 20% dilution of Baytril in half ml and shot 1/4ml in each nostril (1/4 ml 20% solution Baytril)
Keep that animal at 86 degrees
Good luck with your animal.