Every week or so, you should probably allow the stock to get very low in the crockpot without replacing water. Turn off the crock, then clean it. Then start all over again. Switch crockpots every so often so one isn't working for weeks at a time. The most nourishing stock/broth comes from the most nourishing bones. Grass-fed, pastured, etc. If your stock does not gel, consider adding good-quality gelatin. GAPS people with very sensitive digestive systems may find long-simmered stock too rich. If this is you, don't let the stock keep going for hours and hours or days.
Perpetual Stock or Broth https://traditionalcookingschool.com/food-preparation/recipes/perpetual-stock-broth/