If a pile is not heating (see next section), the food supply (carbon and nitrogen), moisture level, and aeration needs to be considered. If the pile is mixed and heating occurs, then either aeration (oxygen) was limiting, or the layers and sources needed to be mixed. If no heating occurs and water may be limiting, add water. If both air and water are present and the pile has been mixed, either composting is finished or more nitrogen or carbon needs to be added.