Prewashing a coral in 3% hydrogen peroxide can help to oxidize any dead organics and issue from the coral. It is a very strong oxidizer so we recommend using a very conversative amount.

The current recommended amount: 30 to 40ml/gal tank water
The current recommended time: 5-10mins.

Direction:

Mix the above ratio into a clean container and add the coral that need to be treated. Lightly turkey baster around the coral, including into cavity where you see dead tissue. You'll see "bubbling" happening after a couple of minutes; this is the oxidizing property of H2O2 at work. If it's bubbling too fast, immediately take the coral out. You DO NOT want it to oxidize too much.

Do the same procedure on corals after doing the kfc dip. This will help clean the coral before putting it back into the tank. Do NOT reuse any dip water. You should always make a new batch of H2O2 water after it's used.

Source - kungfucorals.com https://kungfucorals.com/blogs/news/pre-wash-and-post-wash-with-hydrogen-peroxide