bonsai...
Akadama soil is used by bonsai people for re-establishing transplanted wild plants, or large transplants. Its a kind of clay soil with large, firm gravel-sized particles. Its sort of like kitty-litter (kaolinite clay).
I don't know why you're using paper towels on the top of the soil, doesn't sound practical, but I use nylon window screen, and I have no mold issues. Its easy to clean too.
Some organic soils are very prone to molds and mildews, but the ones with a peat moss base tend to resist molds. It may be time to change soil. You can also fight molds by increasing the air circulation with a fan. There are organic fungicides like Serenade and copper soap as well.