My 3 chickens dont have the blackish/brown poop with a white cap, that I have recently seen. Theyre poop is always a dark brown, sometimes with a tint of green and is very liquidy, like thick yogurt. Diet:They have half scratch and half pellets always. One banana a day. And free range from morning to dusk when they go into the coop on their own. Should I add something to their diet? Thanks.