white fluffy mold

I work in a warehouse and the when it rains the water pools on the roof and slow drips into the warehouse through the ceiling vent. on a bad rain we can get about an inch of water in a wastepaper basket. Noticed today that there was some white fluffy stuff on the smooth concrete floor in the area where the concrete gets wet . I scraped it with some paper towel and the stuff looked like cotton candy. I wiped the concrete with Fantastic with bleach and 3 hours later I noticed that it has started growing back. Never though it would grow back soo fast. Would putting something like baking soda or cornstarch work to help suffocate the mold and draw moisture from the concrete? Is it mold or is it efflorescence ? sorry no photo.