I don't have any suggestions, just a similar problem!
I got rid of the top few inches of soil from a hibiscus I bought from Home Depot and replaced it with some organic potting soil, but every couple of days I scrape off some of the top layer because it's getting fuzzy... The water also smells terrible when it comes out of the plant, I should probably try completely re-potting it.
The soil I use is the Organic Choice Potting Mix from Miracle Gro. I'll get back to you after I replant it with just the Miracle Gro.