Calculate pool volume and pump flow rate — run time is the ratio.

Divide your pool’s gallon capacity by your pump’s gallons-per-hour flow rate. That gives you the hours needed to turn over all the water once, which is the gold standard for filtration.

To get your pool’s volume: length × width × average depth × 7.5 (for rectangular pools). For round pools, it’s diameter² × depth × 5.9. For irregular shapes, break it into rectangles and circles, or just Google a pool volume calculator.

For pump flow rate: check the label on your pump — it’ll say something like “60 GPM” (gallons per minute). Multiply by 60 to get gallons per hour. But know that actual flow is lower due to pipe friction, filter resistance, etc. If you’re lazy (like me), assume 75% of the rated flow.

Example: 20,000 gallon pool, pump rated at 60 GPM (3,600 GPH). At 75% efficiency, that’s 2,700 GPH. 20,000 ÷ 2,700 = about 7.4 hours. Round up to 8 and call it good in summer. In winter, you can cut that in half — algae grows slower when cold.

If you run the pump longer than needed, you’re just wasting electricity and wearing out the motor. If you run it less, you risk green water. One turnover per day is the sweet spot.

Most pool pumps are oversized anyway, so don’t be surprised if your calculated time is under 8 hours. That’s fine