| Timing | Task | Why |
|---|---|---|
| Same evening (after party) | Test FC and pH | Know your baseline before adding chemicals |
| Same evening | Shock with 1–3 lbs cal-hypo per 10K gal | Destroy chloramines, restore chlorine reserve |
| Same evening | Run filter 24 hours | Remove fine debris from bather load |
| Next morning | Skim surface and vacuum floor | Remove settled debris and sunscreen residue |
| Next morning | Retest FC, pH, and alkalinity | Confirm chemistry is back in range |
| Next morning | Backwash filter if pressure elevated | Restore filter flow capacity |
| Before next swim | Confirm FC is 1–5 ppm | Safe to swim only after chlorine in range |
Every swimmer introduces a significant load of nitrogen-containing compounds — sweat, body oils, sunscreen, cosmetics, hair products, and inevitably some urine. These react with free chlorine to form chloramines (combined chlorine), consuming free chlorine in the process.
The chemistry hit from a party is substantial:
A pool that tests at 1.5 ppm free chlorine the morning of the party may test at 0 ppm by evening. That's the overnight window when algae blooms begin if the shock isn't done promptly.
| Party Size | Shock Dose (Cal-Hypo 65%) | Notes |
|---|---|---|
| Small (under 10 swimmers) | 1 lb per 10,000 gal | Standard dose |
| Medium (10–20 swimmers) | 1.5 lbs per 10,000 gal | Increase for afternoon heat |
| Large (20+ swimmers) | 2–3 lbs per 10,000 gal | Treat like a mild algae event |
| FC already at zero | 2–3 lbs per 10,000 gal minimum | Algae may have started |
The fastest way to prevent the post-party green pool: shock the evening of the party, not the next morning. Algae spores that survived depleted chlorine overnight have an 8–12 hour head start. The difference between an easy fix and a 3-day algae recovery is often whether you shocked that same evening.
SplashLens lets you tag maintenance events — log "20-person pool party" with the chemistry readings before and after. Over time, you'll know exactly how much your pool needs by swimmer count, which takes all the guesswork out of post-party treatment.
Open SplashLens Free →Every swimmer introduces nitrogen compounds from sweat, sunscreen, and body oils that react with free chlorine to form chloramines, consuming chlorine in the process. 10 swimmers for an afternoon can consume 2–3 ppm of free chlorine. Large parties can deplete chlorine entirely.
1 lb per 10,000 gallons for a small party (under 10 swimmers). 2–3 lbs per 10,000 for a large party or if chlorine is already zero. Adjust pH to 7.2–7.4 before shocking and add after sunset for maximum effectiveness.
Possibly — cloudy water indicates chloramine buildup, fine bacterial growth from depleted chlorine, or oil and debris from bather load. Shock immediately, run filter 24 hours, and the pool should clear within 24–48 hours. Add clarifier if still cloudy after 48 hours with adequate chlorine.
After shocking, wait until free chlorine is below 5 ppm (typically 8–12 hours after a standard 1–2 lb dose). Always test — don't assume based on time. pH should be 7.2–7.8. At very high shock doses (3–5 lbs per 10K), wait 24 hours and test before re-entry.
Yes — backwash the next morning (sand or DE filter) or rinse the cartridge. Heavy bather load significantly loads the filter with fine oils, bacteria, and debris. A clean filter at full capacity handles the recovery period much more efficiently than a partially clogged one.