Algae definitely will pick up the floc and float it about when exposed to sun and creates bubbles. There are likely other micro organisms that have ballast bubbles that get caught up in the floc as well and can lift it. Then there is always the possibility of adding salts that causes gasses to come out of solution, or even react with things in the water column creating gasses that would get trapped in the floc and lift it. In any case, it should settle once it is dark or the gasses dissolve back into solution.