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Testing spas practice questions

29 questions from the pool operator (cpo) practice test.

Testing spas practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

What is the main limitation of the orthotolidine (OTO) chlorine test?

  1. It measures only free chlorine, not total chlorine
  2. It reads the pH and chlorine as a single number
  3. It works only when cyanuric acid is present
  4. It measures only total chlorine, not free chlorine
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D. It measures only total chlorine, not free chlorine

OTO turns yellow with total chlorine and cannot show how much is free, so combined chlorine cannot be found. DPD separates free from total.

Reference: PHTA Pool & Spa Operator Handbook, water testing chapter

After the free chlorine reading is taken with DPD No. 1, how is total chlorine found in the same sample?

  1. Add phenol red and read the color again
  2. Add a neutralizer and read the color again
  3. Wait ten minutes and read the color again
  4. Add DPD No. 3 and read the color again
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D. Add DPD No. 3 and read the color again

DPD No. 3 releases the combined chlorine so the sample then shows total chlorine; the increase in color is the combined chlorine. A neutralizer would remove the chlorine altogether.

Reference: PHTA Pool & Spa Operator Handbook, water testing chapter

To test a heavily chlorinated pool, an operator mixes 1 part pool water with 3 parts distilled water. The diluted sample reads 3.5 ppm free chlorine. What is the pool's free chlorine level?

Answer in ppm.

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14 ppm

The sample is 1 part pool water in 4 parts total, so the multiplier is 4. Pool level = 3.5 x 4 = 14 ppm.

Reference: PHTA Pool & Spa Operator Handbook, water testing chapter

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