Turnover and run-time calculator
Two numbers decide a pool's run time: how fast the water moves and how much filter it has to move through. This gives you both, and flags the filter that is being driven past the point of catching anything.
Turnover is how long the pump needs to push a pool's worth of water through the filter once. Two turnovers a day is the working habit on a residential pool.
One turnover
7.3hours
- Run time for two turnovers
- 14.7 h/day
- Filtration rate
- 1 gpm/ft²
- Filter loading
- in range
A filter driven above about 15–20 gpm per square foot of media passes dirt straight through, whatever the pressure gauge says. If your rate is high, the answer is more filter area or a slower pump speed, not a longer run.
Turnover is a filter question
Turnover asks how long the pump needs to send one pool’s worth of water through the filter. It is not a promise that every molecule has been filtered — mixing means a single turnover treats roughly two-thirds of the water — which is why two turnovers a day is the working habit rather than one.
The number nobody checks
Filtration rate — gallons per minute per square foot of media — decides whether the filter is actually catching anything. Push water through too fast and fine debris goes straight past the sand while the pressure gauge sits reassuringly normal. That is the most common cause of a pool that is clean on paper and cloudy in daylight.
| Rate | Reading | What to do |
|---|---|---|
| Under 15 gpm/ft² | In range | Nothing |
| 15–20 gpm/ft² | Top of range | Drop pump speed if you can |
| Over 20 gpm/ft² | Over-driven | More filter area, or slower — not a longer run |
Measure the flow, do not read the plate
The gallons per minute on a pump label is what it does at zero head. Real flow comes off a flow meter, or from the pump curve at your measured head — the pump sizing tool estimates the head for you.
What a longer run does and does not fix
Running longer fixes an under-filtered pool. It does not fix an over-driven filter, a channelled sand bed or a torn cartridge, and it certainly does not fix chemistry. If two turnovers a day still leave the water dull, take the filter apart — start with cleaning it properly.