The growth that you see on the sides of the well, and falling to the bottom, are probably a species of iron bacteria growing in the well.
In this video, you can see a red growth on the PVC casing. This is probably another species of iron bacteria.
Bacteria Found in Wells
Wells often contain bacteria, although not all bacteria will cause health problems. Coliform bacteria are the major culprit when it comes to waterborne bacterial illnesses. Some indications of coliform bacterial contamination are changes in the water's taste, odor, or appearance. For more information on testing for bacterial contamination and other contaminants see the well treatment section of this site.
There are other types of bacteria that may be present in a well that do not cause disease. Iron and Manganese bacteria can cause nuisances and clog or damage well equipment, but will not typically cause illness. These bacteria create a bio-film, or slime, that can cause well piping to clog, pumps to become damaged, and can hinder treatment methods used for harmful bacteria. Iron and manganese bacteria get energy from oxidizing dissolved forms of the metals they are named for. The bio-film that protects the bacteria is red for iron bacteria, and black for manganese bacteria.
Treatment for these bacteria can be difficult as the bio-film protects the bacteria from all but high doses of shock chlorination or acid treatments. The best method of treatment is prevention, make sure to hire a reputable well driller, and be sure that they treat their equipment, well casing, and even water used in the drilling process with a strong disinfectant. If you do find that you have iron bacteria in your well, you can shock chlorinate the well, but it is likely that the iron bacteria will return. You can also install a method of continual chlorination treatment, which should provide a permanent solution as long as treatment continues. A certified well driller can provide chlorination and acid treatments as well.