I found this article by Albert Thiel on the use of Vitamin C for treating coral infection.
When a coral is infected you can try the following method:
Remove the brown slime stringy material (you can often siphon most of it out). Do this while the coral is still in the aquarium. Hold the siphon an inch or so away from the slime and start it up. Dump whatever you siphon out into a bucket. Do not reuse the water in that bucket. It is laden with elements and chemicals you do not want back in your tank, besides the slime that you removed and that you do not want in the tank either. Note that sometimes you need to siphon this off several times, hours apart or on consecutive days. Slime may reappear and needs to be removed.
Dip the affected area in fresh water for about one minute maximum. This is optional. Vitamin C treatment alone (as described below) is usually all that is needed.
Clean the affected area with a real soft brush wiping any brownish material you see off the coral.
Rub some powdered Vitamin C on the affected area. Hold the coral out of the water for a minute or two t o le
Treat the entire tank with Vitamin C at the therapeutic dosages recommend in the Vitamin C document in the TAT Web site Library and also in the Latest and Newest article section. Both gives complete details on how to use vitamin C and what kind you need. See below for a link to the Libray.
Keep treating the tank with vitamin C for at least 14 days. This is most important if you want to achieve the results you need to achieve: healing of the coral and eventual regrowth of the polyp in most cases.
Aim good and strong water current at the coral's affected area so it does not become reinfected. There are no guarantees but, the use of Vitamin C will, in the majority of cases, prevent reinfection based on my long time experience with using C in high dosages.
