Diarrhea in 5 day old chick...

Is there anything I can do for her? She's the "runt"...significantly smaller than the other 5. She's acting ok, eating and drinking. But she's got diarrhea for consecutive poops. It's not like any of the pictures I saw on the infamous poop link. It's medium to dark brown in color, has some bubbles in it, and smells awful. Should I be worried? Can I give her something to eat that will make it stop? They are on medicated chick start and grow, and I give them a treat once a day...either boiled egg or some bugs from the yard. I tried yogurt once but none of them liked it. They have a continuous supply of grit. I have also added ACV to their water, which they've had since yesterday. If she poops again and it's the same, I'll take a picture and post it here...that is if I can take the picture before one of the babies steps in it!