Black algae can turn a clean pool into a never-ending battle, and the worst part is you might be spreading it yourself without realizing it. We dig into what “black algae” really is (often cyanobacteria), why it clings so stubbornly to plaster, and why the usual quick shock routine often fails unless you do the one step most people skip: aggressive brushing to break the protective heads so chemicals can reach what’s underneath. We also get specific about transmission and cross contamination....