I did have mold issues this summer when it got hot, that seemed to get all the mold spores activating like crazy. I kept it in check by using up each batch promptly (1 to 3 days) and cleaning out the container (I use a large glass jar) thoroughly after each batch.
Now that it's cooler I no longer have that problem and can use leftover FF to help activate the next batch.
Now that it's cooler I no longer have that problem and can use leftover FF to help activate the next batch.