Gritty Pooh in a 12 mo. old?

Hi. For the last couple of weeks my daughter has had gritty almost watery looking pooh on occasion. It seems to cause diaper rash more than usual. What could be causing this? Is there a known culprit that causes gritty pooh? (Like blueberries cause dark pooh and carrots make orange pooh, bananas cause little black squiglies, etc.)