Blue Rat

Question
My Blue has developed purple scabs on her back a few weeks ago, which I thought might be dry skin. Yesterday she seemed a bit tired, yet today she had dark brown crust around her eyes, and no energy. I gave her a gentle bath to get her eyes open and clean her up, and afterwards she started bleeding from her nose... it's stopped though. Recently I purchased a baby dumbo, and switched their water to KMR milk replacement for kittens, which I've used in the past to boost thier nutrients, and now for this baby dumbo. All the other 3 are in fine health but my Blue.

Answer
 The 'blood' is probably porphyrin, which is the rat's normal red-colored mucus that can appear around the eyes and nose at times of stress or illness.  The scabs could be due to external parasites such as mites or lice, which would also explain the tiredness if the infestation is severe.  I would recommend treating her with Advantage or Revolution, just one drop on the back of her neck right at the skin then another in two week should take care of any external parasites.  If that doesn't help, you should take her to the vet for an exam and some other suggestions.  I would not recommend swapping their water for milk; though giving them KMR can help with some nutrients they still need regular water and food.  A good product to get some weight back on is NutriCal, which can be bought from a vet or online.  I hope she gets better soon, good luck!