Infection/Diarrhea

Question
Hi. First I got two rats about a month ago. Last Wednesday one started acting kind of funny (real slow like she was extremely tired) and had some red stuff coming out of her eye (which i looked up and it said it was nothing to worry about). Then on Thursday she started having trouble walking, (she'd try but kept falling over), and by Friday she couldn't even hold her food. I did some more research online and we think she got an ear infection. I'm trying to find out was it caused by something I did? and if so is there anyway i can prevent it from happening again (my other rat is fine).
Well I ended up taking my rat to the pet store, where they said they could take care of her, and let me get another (younger) rat (Riley). Riley seems to be getting along with my other rat good, but seems to have diarrhea now. Is there something I can give her to help her with this? Should I  separate them for a while?
Thanks for your help.
Oh, I'm also feeding them this block food for rats from the pet store, Papaya treats, and these baked cru-sa-ent things.  

Answer
Are you saying you no longer have the rat that was sick? You returned it to the pet store?

Also, please refer to my site, sandyscrittercity.com and refer to rat illnesses to learn more about the red discharge from the eyes and nose. This is NOT always nothing to worry about. In fact, it is a sign that the rat is stressed. When the rat has other signs of illness along with the excessive red discharge (porphyrin) this is indeed a sign something is wrong. It is nothing to be worried about and some traces of it are normal as long as this is something the rat always has and doesnt display signs of illness along with the red discharge.

The sick rat you had could easily be treated with antibiotics if she had an ear infection.

As for the new rat, you should have done a quarantine for three weeks before putting them together.  Please see about proper quarantine on my site.  Its too late now, however. If the rats were already together, if the new rat is sick, it has exposed the other rat to whatever she may have.  The loose stools may be illness but it could be stress from being put with a new rat in a new home.  
Try giving your rat puffed rice and dried oatmeal flakes for the loose stools. Again, please read over my site. I am sure you will find alot of info that you are looking for on proper rat care along with proper diet.