Even if it is mildew use a mild cleaner or bar keepers friend. Bleach can damage it. I went to several manufactors to check. Use dish soap, or a spray cleaner.
Hibiscus moscheutos aka Southern Belle hibiscus or Swamp hibiscus. It's a hardy perennial hibiscus that likes fun sun and a moist spot in the garden. Blooms like crazy. Makes lots of seeds that are easily dried then planted to make tons of more plants to share.