If you have been away, were the rest of the family members? Was the house shut up? That, combined with the lights being left on will be the culprit.
I should think the water chnages plus added oxygen will see them coming right (hopefully) over the next day or two.
Others have mentioned that white cobwebby algae before. Remove it by hand, or siphon it up, and see if it returns once conditions are back to normal.