Try some yogurt and see if the probiotics in there will help with the runny poo. If not..you may need more than the medicated feed and have to put them on antibiotics or treat them for coccidiosis. Make sure to keep their little vents clean and I'd put a bit of vaseline around each so the poo doesn't stick to them and stop them up.
This is a post from JennsPeeps about poop that was on 9/25/2008. I bookmarked it so I could come back to it if mine ever got poo problems!
https://www.backyardchickens.com/forum/viewtopic.php?id=91786&p=2
There are a couple different types of chicken poo:
1. normal/typical - it's firm, brown with white urea (bird "pee") on it, and looks like it was excreted through a round nozzle
2. cecal - stinky, stinky, stinky! This is runny and you will know it when you see it. OMG it stinks. It comes from a loop in their intestines. Did I mention it smells bad? It's normal, too. Happens roughly every 5-6 poops.
3. bright green - indicates bird is not eating enough and dropping is green due to bile not being sufficiently diluted by excrement
4. diarhea - different from cecal because of frequency
5. bloody - indicates serious problem, potentially cocci
6. watery - indication of too many treats with high moisture content. My girls get this when they eat too many grapes.
Good info and concise and I could remember where to look for it
...Hope it helps you too!