Enter your pool, the guest list, and the hours — get the pre-party boost and the morning-after recovery dose.
Why parties crash chlorine
Chlorine's job is oxidizing organic stuff, and a party is an organics delivery event: sunscreen film, sweat, grass off feet, the occasional juice box casualty. Each swimmer-hour adds load, and the sun keeps taking its usual share on top. The pool that "was fine yesterday" reading zero the morning after a party isn't broken — it did exactly its job and ran out.
A worked example
15,000 gallons at 3 ppm, twelve swimmers for four hours: pre-load to ~5 ppm the night before (about 32 oz of 12.5%), expect the party to burn 2–3 ppm, and plan on a similar-size recovery dose after the retest. Total cost of a perfectly clear party pool: about a half gallon of chlorine and four minutes of testing.
The host's checklist
Night before: dose to top of range, run the pump. Day of: pump on all day, skim before guests arrive. After: retest (the report card grades everything at once), dose back to target, pump overnight. Skip the after-dose and the next 48 hours often produce the season's cloudy spell — the wait-time tool covers when it's swimmable again.
Frequently asked questions
Should I add chlorine before or after a pool party?
Both, ideally: raise free chlorine to the top of your normal range the night before (never shock-level right before guests), then dose again after everyone leaves — a crowd consumes chlorine fast through sunscreen, sweat, and sheer body count.
How much chlorine does a pool party use up?
Rule of thumb: each swimmer-hour consumes meaningfully more chlorine than an empty pool loses to sun. A dozen kids for four hours can strip 2–4 ppm from a typical backyard pool — which is why the morning-after test so often reads near zero.
Can people swim right after I add the pre-party dose?
Dose the evening before and it's a non-issue. If you must dose day-of, keep it a normal (not shock) dose with the pump running and give it a few hours — the wait-time tool has the specifics per chemical.
The water turned cloudy during the party — what now?
Normal after a crowd: sunscreen and organics overwhelm the chlorine temporarily. Dose to the top of range after guests leave, run the pump overnight, and it usually polishes clear by morning. Persistent cloudiness = run the cloudy pool diagnostic.