Use stabilized chlorine for outdoor pools, unstabilized for shocking.

Stabilized chlorine has cyanuric acid (CYA) mixed in, which protects the chlorine from breaking down in sunlight. Unstabilized chlorine does not.

If you have an outdoor pool, you want stabilized. Without CYA, you’d be adding chlorine constantly because the sun burns it off in hours. Most pool tablets (trichlor) and dichlor granules are stabilized.

If you’re shocking or have an indoor pool, go unstabilized. Too much CYA buildup locks up the chlorine — it stops working. Calcium hypochlorite (cal hypo) and lithium hypochlorite are unstabilized. They hit hard and leave no CYA behind.

The trap: using only tablets without testing CYA. Stabilizer doesn’t evaporate. After a season of tablets, your CYA can hit 100+ and your chlorine won’t do anything. Switch between stabilized and unstabilized depending on what your pool needs.

Bottom line: tablets for maintenance in sun, cal hypo for shock, and test CYA monthly.