What's the best way to handle pool algae — prevention or cure?

Prevention beats cure. For an existing green pool, you’ll need something to kill the algae — harsh chemicals usually means chlorine, but you can use a non-chlorine shock like potassium monopersulfate or an enzyme-based algaecide. They’re gentler on skin and won’t bleach your swimsuit. However, if you have a full-on green swamp, none of the gentle stuff will cut through fast enough — you’ll have to brush, vacuum, and circulate constantly while the non-chlorine shock works, as it’s slower than chlorine.