Can I shock a green pool without draining it?

Yes, but it’s not a one-and-done deal. Add a heavy dose of pool shock (calcium hypochlorite granules work well), run the pump 24/7, and brush like crazy. The shock kills the algae, then your filter catches the dead stuff over days, requiring multiple backwashes. Test water first, adjust pH to 7.2–7.4, and check cyanuric acid—if it’s too high, partial draining may help. Draining risks liner damage, so shock and scrub is almost always worth trying first.