I have 1 bird that has a very pale comb as well as the skin around her face. Why is this
Anemic conditions arise when blood is deficient in red blood cells. The face gets pale, they lack energy, and lose weight. If the condition continues the bird will eventually die. Red blood cells are made from iron, B-12, protein, etc. Red blood cells transport oxygen and carbon dioxide from the tissues of the body. Without oxygen, there can be no conversion of nutrients into energy. What is lost through digestion and excreted in droppings is replenished in diet.
Diseases like Coccidiosis, intestinal worms, and bacterial infections can cause enteritis which effects the intestinal tract and bird's absorption of nutrients. Mites are blood suckers and can also cause anemic conditions. Lots of people think blood has to be seen in droppings for Coccidia to be present, and that is not so.
Depending on what you observe with the bird, and all those possibilities I mentioned, you have to consider all those conditions to be the source of the problem. First, treat for Coccidiosis and intestinal worms, check between feathers all over the bird for mites/lice, then supplement water with poultry vitamins/minerals-electrolytes and Probios. In fact, it id beneficial to supplement drinking water with poultry vitamins 3 times a week.