There have been some experiments testing H2O2 for use treating marine velvet. Here is the relavent passage from this article,
http://www.reefkeeping.com/issues/2004-07/sp/feature/index.php
"This is one of the newest ideas for treating Amyloodinium ocellatum and, in my mind, one of the most interesting and promising as well. The first study used 20 juvenile Pacific Threadfin (Polydactylus sexfilis) suffering with an infection of Amyloodinium ocellatum. They were randomly divided into four open water tanks. One tank was the control and received no treatment. The control fish were examined and found to have a mean of 16.6 ± 16.2 trophonts per gill biopsy. The fish that were to be treated with varying levels of hydrogen peroxide were also examined and found to harbor a mean of 35.6 ± 38.7 trophonts per gill biopsy. Water flow to the three treatment tanks was stopped and they were dosed with hydrogen peroxide at concentrations of 75, 150, and 300 ppm. The fish were exposed for thirty minutes and then the water flow was returned to rid the tanks of the hydrogen peroxide. Within one hour of treatment, all the fish exposed to 300 ppm hydrogen peroxide had perished, but the fish exposed to only 75 and 150 ppm tolerated the treatment without any deaths. The surviving fish were examined immediately after treatment and found to harbor no more parasites. They were re-examined the following day. The treated fish were still infection free while the untreated fish were found to have an increase in the trophonts counted.
Another test was set up at the facility where the sick fish were obtained. Scientists used a grow out tank that contained fish infected at a rate of 16.3 ± 13.0 trophonts per gill biopsy. These fish were exposed to 75 ppm hydrogen peroxide for thirty minutes. One day after exposure, the trophonts' count dropped to 4.7 ± 0.6. After six days, the count was down to 1.0 ± 1.0. At this point, the fish were retreated with 75 ppm hydrogen peroxide for another thirty minutes. The day after the second treatment, no trophonts could be found. Because the study's participants were unsure of the effect of hydrogen peroxide against tomonts, they transferred the fish to a clean tank at this time.
Some of these same people then prepared an experiment on Mullet (Mugil cephalus) fry. They first studied hydrogen peroxide's effect on healthy fish. Three groups of ten healthy fish were exposed to 75, 50, and 25 ppm hydrogen peroxide for thirty minutes. After 24 hours, the survival rates were 20, 50, and 70% respectively. They then decided to test 25 ppm hydrogen peroxide on a large larvae-rearing tank. This tank held 3000 liters of water and approximately three fish per liter. The facility had been experiencing 200-1000 deaths per day from Amyloodinium ocellatum for one week prior to the test in this vessel, while the standard daily mortality should have been 0.002%. The fish were treated for 30 minutes with 25 ppm hydrogen peroxide. Within three days of the exposure, mortality dropped to less than 10 per day.
Now before you all go running off to the medicine cabinet, please remember that this treatment is experimental at best. It can easily be overdosed and cause mass mortalities. I would wait until further research has been performed to test the tolerance of various marine ornamentals to hydrogen peroxide exposure. Just to be clear, I am not currently recommending the use of hydrogen peroxide. If you choose to experiment and use it, you could very well be risking the lives of every inhabitant in your aquarium. I mention it only because it is promising, and as something to keep an eye out for in the future, after additional testing has been done. If you wipe out your aquarium with this treatment, don't come crying to me later."
