I feed high fructose corn syrup. I've never seen it get sour or moldy.
At 11.55 lbs to the gallon, maybe its too thick to ferment. No mixing.
I've fed it now for 15 years to thousands of colonies. Do well on it. I
imagine you could get fumidil to mix with it. Can't say, I don't use it.
Keep unused portion sealed and it will be good next season. It does
crystalize, but melts easily with heating.