Will Your Pool Survive
Your Vacation?
Every summer, thousands of owners come home to a green pool. Chlorine burns off on a predictable clock. This simulator runs your pool day-by-day against your real local forecast, shows you which day it turns green, and hands you the plan that saves it.
Day 1 → Day 7 · this is what neglect looks like
Set up your trip
Four quick questions. Guesses are fine; the simulator is built to work with what you know.
Optional. Without it we assume typical summer sun. Your ZIP is only used to fetch weather.
From a test strip or kit. A guess is OK.
Your pool's day-by-day future renders here: water color, chlorine gauge, and the verdict.
Day 1
Protected
Move the green day
Flip a switch, watch the simulation re-run. This is how you engineer a surviving pool.
Your pre-departure survival plan
Personalized to your pool, your setup, and your trip. Do these the day before you leave.
Estimates, not guarantees. Heat waves and equipment failures happen, so the plan is built with margin: a pool that follows it comes home blue even when the simulation runs optimistic.
You're not alone
The same post appears in every pool forum, every August
"Left for a week on vacation. Came home to green algae."
"Came home from vacation… what happened?"
"Going on vacation for 2 weeks. What do I do?"
How Long Can a Pool Go Unattended in Summer?
Typically 2–4 days at everyday chlorine levels before algae risk begins, and 5–8 days if you raise chlorine high the night before leaving. A running salt system or a loaded tab floater extends that, and a cover roughly doubles everything. The exact number for your pool depends on stabilizer, sun, and the week's weather, which is what the simulator above computes.
| Your setup | Everyday chlorine | Boosted before leaving |
|---|---|---|
| No stabilizer (CYA 0) | Under 1 day | 1–2 days |
| Liquid chlorine, CYA 30–50 | 2–4 days | 5–8 days |
| Tabs + loaded floater, CYA 60–80 | 4–6 days | 7–10 days |
| Salt system running | As long as the power holds. Boost before leaving as outage insurance | |
Typical full-sun summer conditions. A solar or solid cover stretches every number above by roughly 2–3×.
The Average Pool, State by State
We ran the same simulation for a typical pool in every state: 15,000 gallons, everyday chlorine, stabilizer at 40, full sun, nobody home. The number is the day the water turns visibly green. Drag the month and watch the country change color.
Tap a state for its numbers.
Days shown are when the standard pool above turns visibly green, using NOAA-derived average daily highs for each state and month plus a latitude-based clear-sky UV estimate. Your pool will differ: run the simulator with your numbers.
The Science in Three Numbers
35 min
Chlorine's half-life in direct sun
With no stabilizer (CYA), most chlorine is gone in a single afternoon.
7.5%
The safety floor
When chlorine drops below 7.5% of your CYA level, algae starts winning.
3–8 hrs
Algae doubling time
Below the floor in warm water, "perfect Tuesday" becomes "green Thursday."
The simulator runs that math day by day: UV loss scaled by your stabilizer, sun exposure, and real forecast, plus replenishment from tabs or a salt cell, then the algae clock once the floor is crossed. It reports a conservative window rather than a fake-precise single day.
Method: the free-chlorine/CYA relationship documented by the Trouble Free Pool community. Weather data from Open-Meteo.
The 5 Ways Pools Die on Vacation
- 1
Leaving at "fine" chlorine. 3 ppm is fine for today. Unreplenished, it burns off in 2–3 sunny days. Leave high instead, dosed after sunset.
- 2
The floater runs dry. Three tabs last about 4–6 days. On a two-week trip it empties at the halfway mark.
- 3
The salt cell quietly stops. A power blip halts production and nobody is home to notice. Banked chlorine is your insurance.
- 4
A heat wave hits while you're gone. A 95°F week eats chlorine far faster than the 82°F week you planned for. That's why this tool reads your actual forecast.
- 5
Shutting the pump off "to save power." Stagnant warm water is an algae incubator. A few dollars of electricity is the cheapest pool insurance there is.
Frequently Asked Questions
How long can a pool go without chlorine?
Once free chlorine actually hits zero, algae can take hold within 24–48 hours in warm water. The real question is how long your chlorine lasts, and that depends on your stabilizer, sun, temperature, and replenishment. That countdown is exactly what the simulator computes for your pool.
Should I shock my pool before vacation?
Yes. Raising free chlorine toward roughly 40% of your CYA the night before you leave is the single highest-value move. Use liquid chlorine, dose after sunset, and use our chemistry calculator for the exact amount. The simulator shows how many protected days it buys.
Will a floater with tabs keep my pool clean for two weeks?
Usually not on its own. Three tabs add roughly 1–2 ppm per day to an average pool and last about 5–7 days. Two-week trips generally need the combination: high starting chlorine, a loaded floater, a cover if possible, or one mid-trip chlorine drop. (Tabs also add stabilizer, which is fine for a trip but not a year-round plan.)
Should I leave the pump running while I'm away?
Yes, on its normal schedule. Circulation is free algae defense. Never shut the system down for a summer trip.
How accurate is this simulator?
It runs the same free-chlorine/CYA framework used by the largest pool-care communities, against your real forecast (up to 16 days out). Because pools vary, it reports a conservative window rather than a fake-precise single day, and it always pairs the verdict with the plan. A pool that follows the plan comes home blue even if the sun ran hotter than forecast.
What if I come home to a green pool anyway?
Don't drain it. Green pools are almost always recoverable. Start with our shock calculator for the right dose, run the pump 24/7, brush daily, and keep chlorine at shock level until it clears (mild green: 1–3 days; full swamp: about a week). Rather hand it off? Find a verified pool pro.
Keep Your Pool Clear By Planning Ahead
One mid-trip visit from a local pro resets your pool's clock completely, at a fraction of what a green-pool recovery costs.
Related: Shock Calculator · Safe to Swim Checker · When to Close Your Pool