How long after shocking a pool can you swim?

When free chlorine is back to 5 ppm or lower, which after an evening shock is usually by the next morning. A heavy shock to clear algae can take a day or two to come down.

The pH matters too. Shock can push it around, so check that it is back between 7.2 and 7.8 before anyone gets in.

Because shock level chlorine is several times what you swim in. It stings eyes, irritates skin, bleaches swimsuits and is hard on hair. The point of shocking is to briefly run the chlorine far above normal to burn through algae and contaminants, then let it settle back down.

The chemical itself deserves respect before it ever reaches the water, too. The CDC is clear that pool chemicals should be stored cool and dry, kept apart, and never mixed with each other.

Test it. A DPD test kit, which is what the CDC recommends for home pools, reads free chlorine accurately at the high levels you get after a shock. Most test strips top out low and cannot tell you whether you are at 5 ppm or 15.

You are looking for free chlorine at 5 ppm or lower, at least 1 ppm (2 ppm if you use stabilizer), and pH in range.

Yes. Chlorine shocks, whether granular or liquid, all mean waiting for the chlorine to come back down. A non chlorine shock, the potassium monopersulfate kind, is different: its label usually allows swimming soon after, often within about 15 minutes to an hour. It does not kill algae the way chlorine does, though, so it is for routine freshening, not a green pool.

Whatever you use, the label on the bag is the final word on the wait.

Because the sun destroys free chlorine. Shock added at midday loses a lot of its strength to sunlight before it gets to work. Added after sunset, it has all night to do its job, and the chlorine has usually settled back down to a swimmable level by morning, which is exactly when you want it.

Wait until chlorine is back near normal, usually the next day. Most algaecides are weakened by very high chlorine, so adding them during a shock wastes them. Clarifier works best once the chlorine has done its job and the filter is running.

Check the label of the product you are using, since the timing varies between brands.

Usually the next day, once the dead algae has settled to the floor. Vacuum slowly so you do not stir it back up. If there is a lot of it, vacuum to waste if your filter allows it rather than pushing it all through the filter. Then clean the filter. If the pool was green enough that you are vacuuming up a layer of dead algae, a green pool cleanup takes that whole job off your hands.

About once a week in a Florida summer, and after any heavy rain, a pool party or a cloudy spell. In winter, every couple of weeks is often enough. The water tells you: if chlorine is dropping fast or the pool looks dull, it needs it.

For our weekly pool service customers this is part of the visit, and the chemicals are in the monthly price.