when you talk about hard, is it those super hard like rock type?? If yes, perhaps is the food that you feed him that causes it.
I realised for Iggy, if I feed him spinach, he poos really soft stools but if it's broccoli/carrots, the poo gets slightly hard like marble size type but when you press on it, it's soft.
And, Iggy still dont't really drinks water up to today. So 80-100m is pretty good to me!!