Maybe the food in whatever amount you are feeding is of greater nutritional value than what you were feeding previously and that threw things off. But maybe not. There are a lot of things that could tip the scales in the algae’s favor. Anything that’s changed in the last few months could be relevant. Adding something that adds nutrients, removing something that removes nutrients. What kind of lights do you have? How old are they? Maybe a shift in spectrum could give algae the edge?