Place chicken bones, onions, celery, carrots, peppercorns, thyme, bay leaves, apple cider vinegar, seaweed, nettle and water into a large stock pot or slow cooker. Bones should be completely submerged so add more water if necessary. Bring to boil, decrease heat and simmer covered for 12-14 hours. The longer the broth simmers the more flavourful and nutrient dense it will be. Skim off any foam that happens to come to the surface. Add parsley at the last 30 minutes of cooking.
Remove from heat and strain the broth through a mesh strainer. Cool to room temperature and pour broth into large mason jars and store in the fridge (up to a week) or freezer (up to 6 months). If freezing, ensure to leave at least 2 inches at the top of the jar in case broth expands. If any fat hardens on the top either leave in the soup or simply scrape off and use for other cooking (this is healthy fat!).
Broth can be used in homemade soup, in place of water to cook grains, sauces, drizzled over cooked veggies, or simply drunk as a 'tea' etc.