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Pool Calculations and Formulas Flashcards

7 cards from real CPO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A sand filter has an effective filter area of 8 square feet. The maximum recommended flow rate for sand filters is 15 GPM per square foot. What is the maximum allowable flow rate for this filter?

    Answer: 120 GPM

    Maximum flow rate = filter area × max flow per sq ft = 8 sq ft × 15 GPM/sq ft = 120 GPM.

  2. A pool water test shows total chlorine = 3.0 ppm and combined chlorine = 1.2 ppm. What is the free chlorine level?

    Answer: 1.8 ppm

    Free chlorine = Total chlorine − Combined chlorine = 3.0 − 1.2 = 1.8 ppm.

  3. What is the recommended cyanuric acid (stabilizer) concentration for an outdoor chlorinated pool?

    Answer: 30–50 ppm

    Cyanuric acid at 30–50 ppm protects free chlorine from UV degradation without excessively slowing chlorine activity.

  4. A community pool has 1,200 square feet of surface area. If the standard is 15 square feet per bather, what is the maximum bather capacity?

    Answer: 80 bathers

    Maximum bather load = total surface area ÷ sq ft per bather = 1,200 ÷ 15 = 80 bathers.

  5. A pool had TDS of 300 ppm when filled; current TDS is 2,800 ppm. What is the TDS increase, and what is the recommended corrective action?

    Answer: 2,500 ppm increase; partially drain and refill with fresh water

    TDS increase = 2,800 − 300 = 2,500 ppm; when TDS exceeds fill-water levels by more than 1,500 ppm, a partial drain and refill is the only remedy.

  6. A diatomaceous earth (DE) filter has an effective area of 40 square feet. The maximum recommended flow rate for DE filters is 2 GPM per square foot. What is the maximum flow rate for this filter?

    Answer: 80 GPM

    Max flow = 40 sq ft × 2 GPM/sq ft = 80 GPM for this DE filter.

  7. A 40,000-gallon pool has a cyanuric acid level of 100 ppm and the target is 50 ppm. What percentage of water must be drained and replaced with fresh water to reach the target?

    Answer: 50%

    Dilution % = (current − target) / current × 100 = (100 − 50) / 100 × 100 = 50% of the water must be replaced.