chicken poop

1 of my chickens sometimes has a light brown poop and slightly runny, looking at other posts its not yellow. is this normal? they've recently been wormed and at the moment are having some apple cider vinegar in their water, all looking very healthy and eating and drinking well. i regulary check them over and all have clean vents am i worrying about nothing? also the other day we bought them a pecking block with corn and mealworms etc in, they went mad for it and i was wondering if they was a cheaper alternative or possibly make ur own?

 

thanks for the link, not sure if its ceacal or signs of blackhead. i take it u can get flubenvet on the internet? is it a wormer? treated mine about a month ago if it is would it b worth seperating the bird to make sure she gets the dose that she needs? we found the others get to it first and don't stop going through the food till they find all of it could b that she never got her share