How old are your chicks? I've never checked for it... Its something that usually jumps out at you. To help prevent pasty butt, add a very small amout of apple cider vinager to their water. I have a smaller quart size (I think) waterer for my chicks. I add about a half a teaspoon to a teaspoon to that. The Apple Cider Vinager will pretty much prevent it, and helps their bodies absorb nutrients better to. I add it to all my chickens water.