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Accuracy

Every dose, checked against the math.

One chemistry engine computes every target and dose in the app, the water check and the free tools. Before each release it has to reproduce 50 reference cases worked by hand from published pool chemistry, and agree with an independent calculator on each one. If a single check fails, the release stops.

Reference cases
50
Worked answers matched
174 of 174
Cross-checks agreeing
91 of 91
Cases updated
Sep 30, 2026

How the numbers are made.

  1. 1

    Targets from your water

    Free chlorine targets follow the FC/CYA relationship: the more stabilizer, the more chlorine the pool needs. Salt pools, hot tubs, bromine and surfaces each get their own ranges.

  2. 2

    Doses from published formulas

    Each product's dose comes from its strength and the pool's volume, using the formulas published with the Pool Math calculator. pH doses account for alkalinity and borates.

  3. 3

    Amounts you can measure

    The exact figure is rounded to something you can pour or weigh (cups, fluid ounces, grams or litres) and tied to the container you buy, like a 1-gallon jug.

The AI coach never produces a number of its own: it explains the engine's results. Where published sources disagree, the choice we made and the reason for it are written down in our chemistry specification.

The independent cross-check.

Every case is also run through a second calculator: a separate implementation of the dosing math, written without access to our engine's code and transcribed from poolcalculator.com's published formulas. Its answer sits next to ours in each case below, and the release stops if the two disagree by more than the rounding of the arithmetic (0.1% for amounts).

Today 58 of 91 comparisons give the same answer. The other 33 differ on purpose, because we made a different, documented choice; for those, our number has to stay inside the stated bound, or equal the published chart value worked by hand.

What this proves, and what it doesn't: both calculators trace back to published pool-calculator formulas, so the cross-check catches arithmetic, unit and transcription mistakes, not a formula that is wrong about real water. That is why every plan asks you to retest after each dose.

Where we differ on purpose

Chlorine strength
Up to 3% apart, on purpose. We follow Pool Math, which accounts for how dense strong chlorine is and that 10% and 12.5% jugs are labelled by volume. The reference scales the dose in a straight line with the label percent. A 3% difference is smaller than the rounding to cups or litres you pour.
Calcium chloride purity
About 6% more, on purpose. Calcium chloride pellets are sold at 94 to 97% purity; we dose for 94%. The reference assumes pure calcium chloride.
Calcium chloride flakes
About 2% less, on purpose. Flakes are labelled 77 to 80% calcium chloride; we dose for 77%. The reference uses pure dihydrate (75.5%).
Weaker acid
About 8% more, on purpose. 14.5% acid is lighter as well as weaker, so it takes 2.34 times the volume of 31.45% acid, not 2.17 times. The reference scales by the percent alone. The plan says to add half and retest either way.
SLAM level
Different on purpose. Our shock level is about 40% of CYA, the published FC/CYA chart. The reference uses poolcalculator.com's own formula (CYA ÷ 6 + 8.5), which runs higher at low CYA and much lower at high CYA. We pin our number to the chart value worked by hand.
Mustard algae level
Different on purpose. For mustard algae we shock at 60% of CYA, the more cautious of the two published levels. The reference uses CYA ÷ 2 + 4.5. We pin our number to the chart value worked by hand.

The reference cases.

50 of 50 pass every check today

“Engine” is computed when this page is built, from the same code that runs in the app. Exact amounts are shown before rounding to cups or grams, so small differences are visible.

Chlorine doses by product and strength

1

Liquid chlorine pool, CYA 40, chlorine a little low

15,000-gallon liquid chlorine pool, plaster

  • FC 3.5
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 82

Worked by hand: +2.5 ppm × 56,781 L ÷ 100 g/L available chlorine = 1,420 mL, about 48 fl oz or 6 cups.

Sources: T5, LSpec §2 FC vs CYA; §6 liquid chlorine

Worked answer and engine result for case 1
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsraise FC, retestraise FC, retest
Dose: raise FC6 cups6 cups
FC minimum33
FC target min55
FC target max77
Engine and independent reference for case 1
Cross-checkEngineRef.Result
10% liquid chlorine, FC 3.5 to 648 fl oz46.7 fl oz2.8% more, by design
FC minimum at CYA 403 ppm3 ppmSame
Top of the FC target at CYA 407 ppm7 ppmSame
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

2

6% household bleach instead of pool chlorine

15,000-gallon liquid chlorine pool, plaster, 6% chlorine on the shelf

  • FC 4
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 82

Worked by hand: 6% bleach is weaker: k = 75.71 × 6 + 0.746 × 36 = 481.1. +2 ppm × 15,000 gal ÷ 481.1 = 62.4 fl oz, about 8 cups.

Sources: T25, T26, LSpec §6 liquid chlorine (weight % at or below 9%)

Worked answer and engine result for case 2
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsraise FC, retestraise FC, retest
Dose: raise FC8 cups8 cups
Engine and independent reference for case 2
Cross-checkEngineRef.Result
6% bleach, FC 4 to 662.4 fl oz62.2 fl oz0.2% more, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

3

8.25% bleach, CYA 50

10,000-gallon liquid chlorine pool, plaster, 8.25% chlorine on the shelf

  • FC 4
  • CC 0
  • CYA 50
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 82

Worked by hand: CYA 50: dose goal 7. k = 75.71 × 8.25 + 0.746 × 8.25² = 675.4. +3 ppm × 10,000 gal ÷ 675.4 = 44.4 fl oz, about 5½ cups.

Sources: T5, T25, LSpec §2 FC vs CYA; §6 liquid chlorine

Worked answer and engine result for case 3
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsraise FC, retestraise FC, retest
Dose: raise FC5½ cups5½ cups
FC minimum44
FC target min66
FC target max88
Engine and independent reference for case 3
Cross-checkEngineRef.Result
8.25% bleach, FC 4 to 744.4 fl oz45.2 fl oz1.8% less, by design
FC minimum at CYA 504 ppm4 ppmSame
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

4

12.5% pool chlorine, CYA 30

20,000-gallon liquid chlorine pool, plaster, 12.5% chlorine on the shelf

  • FC 3
  • CC 0
  • CYA 30
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 82

Worked by hand: 12.5% is sold by trade percent: k = (75.71 × 12.5 + 0.746 × 12.5²) × (1.02 − 0.008 × 12.5) = 977.9. +2 ppm × 20,000 gal ÷ 977.9 = 40.9 fl oz, about 5 cups.

Sources: T5, T25, LSpec §2 FC vs CYA; §6 liquid chlorine (trade % above 9%)

Worked answer and engine result for case 4
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsraise FC, retestraise FC, retest
Dose: raise FC5 cups5 cups
FC minimum22
FC target min44
FC target max66
Engine and independent reference for case 4
Cross-checkEngineRef.Result
12.5% liquid chlorine, FC 3 to 540.9 fl oz39.8 fl oz2.7% more, by design
Top of the FC target at CYA 306 ppm6 ppmSame
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

5

40,000-gallon pool with FC 1: keep out, then chlorine

40,000-gallon liquid chlorine pool, plaster

  • FC 1
  • CC 0
  • CYA 60
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 84

Worked by hand: CYA 60: minimum 5, ideal 8. +7 ppm × 151,416 L ÷ 100 g/L = 10.6 L = 2.8 gal, rounded to 2¾ gal.

Sources: T5, LSpec §2 FC vs CYA; §9 safety; §10 practical amounts

Worked answer and engine result for case 5
CheckWorked answerEngine todayResult
Statusurgenturgent
First stepkeep outkeep out
Dose: raise FC2¾ gal2¾ gal
Engine and independent reference for case 5
Cross-checkEngineRef.Result
10% liquid chlorine, FC 1 to 82.8 gal2.72 gal2.8% more, by design
FC minimum at CYA 605 ppm5 ppmSame
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

6

Cal-hypo 65% adds calcium with the chlorine

15,000-gallon cal-hypo pool, plaster

  • FC 3
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 300
  • Water °F 80

Worked by hand: k = 74.28 × 65 = 4,828. +3 ppm × 15,000 gal ÷ 4,828 = 9.3 oz. Each 1 ppm FC from cal-hypo adds 0.71 ppm calcium: about 2.1 ppm.

Sources: T28, LSpec §6 cal-hypo

Worked answer and engine result for case 6
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsraise FC, retestraise FC, retest
Dose: raise FC9 oz9 oz
Engine and independent reference for case 6
Cross-checkEngineRef.Result
Cal-hypo 65%, FC 3 to 69.32 oz9.32 ozSame
Calcium added by that dose2.12 ppm2.12 ppmSame

7

Cal-hypo pool with calcium 700: switch to liquid

15,000-gallon cal-hypo pool, plaster

  • FC 3
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 700
  • Water °F 80

Worked by hand: CH 700 is above the plaster range, and every 1 ppm FC from cal-hypo adds 0.71 ppm calcium (2.1 ppm for this dose), so the plan switches to liquid: +3 ppm × 15,000 gal ÷ 781.8 = 57.6 fl oz, about 7 cups.

Sources: T28, T3, LSpec §6 cal-hypo; §9 stop the source

Worked answer and engine result for case 7
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsswitch sanitizer, raise FC, retestswitch sanitizer, raise FC, retest
Dose: raise FC7 cups7 cups
Engine and independent reference for case 7
Cross-checkEngineRef.Result
10% liquid chlorine instead, FC 3 to 657.6 fl oz56 fl oz2.8% more, by design
Calcium that 73% cal-hypo would have added2.12 ppm2.12 ppmSame
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

8

Dichlor in a vinyl pool adds CYA with every dose

12,000-gallon dichlor pool, vinyl

  • FC 3
  • CC 0
  • CYA 30
  • pH 7.6
  • TA 70
  • CH 150
  • Water °F 80

Worked by hand: k = 4,149. +2 ppm × 12,000 gal ÷ 4,149 = 5.8 oz, about 6 oz. Each 1 ppm FC from dichlor adds about 0.9 ppm CYA: 1.8 ppm.

Sources: T30, LSpec §6 dichlor

Worked answer and engine result for case 8
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsraise FC, retestraise FC, retest
Dose: raise FC6 oz6 oz
Engine and independent reference for case 8
Cross-checkEngineRef.Result
Dichlor 56%, FC 3 to 55.78 oz5.78 ozSame
CYA added by that dose1.82 ppm1.82 ppmSame

9

Tablet pool with low chlorine: liquid now, not more tablets

10,000-gallon tablets (trichlor) pool, plaster

  • FC 2
  • CC 0
  • CYA 50
  • pH 7.5
  • TA 100
  • CH 350
  • Water °F 84

Worked by hand: Tablets dissolve too slowly to fix a low reading, so the plan uses liquid: +5 ppm × 10,000 gal ÷ 781.8 = 64 fl oz, 8 cups. The same +5 ppm from trichlor (k 6,855) would be 7.3 oz and add 3 ppm CYA.

Sources: T29, LSpec §6 trichlor; §9 stop the source

Worked answer and engine result for case 9
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepsraise FC, retestraise FC, retest
Dose: raise FC8 cups8 cups
Engine and independent reference for case 9
Cross-checkEngineRef.Result
10% liquid chlorine, FC 2 to 764 fl oz62.2 fl oz2.8% more, by design
Trichlor for the same +5 ppm7.29 oz7.29 ozSame
CYA that trichlor would add3.03 ppm3.03 ppmSame
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

Chlorine levels and SLAM

10

Indoor pool, CYA 20

12,000-gallon indoor liquid chlorine pool, plaster

  • FC 2
  • CC 0
  • CYA 20
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 84

Worked by hand: Indoor CYA 20 to 30; at CYA 20 the chart gives minimum 2, target 3 to 5.

Sources: T5, T5b, T14Spec §2 FC vs CYA; §4 indoor CYA

Worked answer and engine result for case 10
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsraise FC, retestraise FC, retest
FC minimum22
FC target min33
FC target max55
Engine and independent reference for case 10
Cross-checkEngineRef.Result
10% liquid chlorine, FC 2 to 430.7 fl oz29.9 fl oz2.8% more, by design
FC minimum at CYA 202 ppm2 ppmSame
Top of the FC target at CYA 205 ppm5 ppmSame
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

11

Combined chlorine 0.8: shock and hold

15,000-gallon liquid chlorine pool, plaster

  • FC 4
  • CC 0.8
  • CYA 40
  • pH 7.8
  • TA 70
  • CH 350
  • Water °F 80

Worked by hand: CC above 0.5 means SLAM; SLAM FC at CYA 40 is 16. +12 ppm × 56,781 L ÷ 100 g/L = 6,814 mL = 1.8 gal.

Sources: T3, T5, T9Spec §2 SLAM level; §3 SLAM

Worked answer and engine result for case 11
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepslower pH, SLAM, retestlower pH, SLAM, retest
Dose: SLAM1¾ gal1¾ gal
SLAM FC1616
Engine and independent reference for case 11
Cross-checkEngineRef.Result
Acid first, pH 7.8 to 7.5 at TA 7010.7 fl oz10.7 fl ozSame
10% liquid chlorine, FC 4 to 161.8 gal1.75 gal2.8% more, by design
SLAM level at CYA 4016 ppm15 ppmdifferent formula, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).
  • SLAM level: our shock level follows the published FC/CYA chart (about 40% of CYA); the reference uses poolcalculator.com's own formula. Ours must equal the chart value worked by hand.

12

Mustard algae raises the shock level

15,000-gallon liquid chlorine pool, plaster, mustard algae

  • FC 4
  • CC 0.8
  • CYA 40
  • pH 7.4
  • TA 70
  • CH 350
  • Water °F 80

Worked by hand: Mustard algae shock level is 60% of CYA: 0.6 × 40 = 24 ppm.

Sources: T6Spec §2 mustard algae shock

Worked answer and engine result for case 12
CheckWorked answerEngine todayResult
Statusurgenturgent
SLAM FC2424
Engine and independent reference for case 12
Cross-checkEngineRef.Result
10% liquid chlorine, FC 4 to 243 gal2.92 gal2.8% more, by design
Mustard shock level at CYA 4024 ppm24 ppmSame
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

13

SLAM at CYA 30 with 12.5% chlorine

10,000-gallon liquid chlorine pool, plaster, 12.5% chlorine on the shelf

  • FC 2
  • CC 0.6
  • CYA 30
  • pH 7.5
  • TA 70
  • CH 350
  • Water °F 78

Worked by hand: SLAM is about 40% of CYA: floor(0.393 × 30 + 0.5) = 12. +10 ppm × 10,000 gal ÷ 977.9 = 102 fl oz, about 13 cups.

Sources: T5, T9, LSpec §2 SLAM level; §3 SLAM

Worked answer and engine result for case 13
CheckWorked answerEngine todayResult
Statusurgenturgent
StepsSLAM, retestSLAM, retest
Dose: SLAM13 cups13 cups
SLAM FC1212
Engine and independent reference for case 13
Cross-checkEngineRef.Result
12.5% liquid chlorine, FC 2 to 12102.3 fl oz99.5 fl oz2.7% more, by design
SLAM level at CYA 3012 ppm13 ppmdifferent formula, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).
  • SLAM level: our shock level follows the published FC/CYA chart (about 40% of CYA); the reference uses poolcalculator.com's own formula. Ours must equal the chart value worked by hand.

14

Green pool at CYA 60: keep out, then SLAM to 24

20,000-gallon liquid chlorine pool, plaster, visible algae

  • FC 1
  • CC 0.4
  • CYA 60
  • pH 7.4
  • TA 80
  • CH 350
  • Water °F 84

Worked by hand: Visible algae means SLAM. floor(0.393 × 60 + 0.5) = 24. +23 ppm × 20,000 gal ÷ 781.8 = 588 fl oz = 4.6 gal, rounded to 4½.

Sources: T5, T9, LSpec §2 SLAM level; §3 SLAM

Worked answer and engine result for case 14
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepskeep out, SLAM, retestkeep out, SLAM, retest
Dose: SLAM4½ gal4½ gal
SLAM FC2424
Engine and independent reference for case 14
Cross-checkEngineRef.Result
10% liquid chlorine, FC 1 to 244.6 gal4.47 gal2.8% more, by design
SLAM level at CYA 6024 ppm18 ppmdifferent formula, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).
  • SLAM level: our shock level follows the published FC/CYA chart (about 40% of CYA); the reference uses poolcalculator.com's own formula. Ours must equal the chart value worked by hand.

15

Salt pool SLAM at CYA 80: lower CYA to 70 first

18,000-gallon salt cell pool, plaster

  • FC 3
  • CC 0.8
  • CYA 80
  • pH 7.5
  • TA 70
  • CH 400
  • Salt 3200
  • Water °F 86

Worked by hand: A SLAM needs CYA 70 or lower: replace 1 − 70/80 = 12.5% (2,250 gal). The refill dilutes FC to 2.6; SLAM at CYA 70 is floor(0.393 × 70 + 0.5) = 28.

Sources: T9, T22, LSpec §3 SLAM preparation; §4 partial drains

Worked answer and engine result for case 15
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepspartial drain, SLAM, salt cell output, retestpartial drain, SLAM, salt cell output, retest
Dose: partial drain2,200 gal2,200 gal
Dose: SLAM4½ gal4½ gal
SLAM FC2828
Engine and independent reference for case 15
Cross-checkEngineRef.Result
Water to replace, CYA 80 to 7012.5%12.5%Same
10% liquid chlorine after the refill, FC 2.6 to 284.57 gal4.44 gal2.8% more, by design
SLAM level after the drain (CYA 70)28 ppm20 ppmdifferent formula, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).
  • SLAM level: our shock level follows the published FC/CYA chart (about 40% of CYA); the reference uses poolcalculator.com's own formula. Ours must equal the chart value worked by hand.

16

Mustard algae at CYA 60

15,000-gallon liquid chlorine pool, plaster, mustard algae

  • FC 5
  • CC 0.3
  • CYA 60
  • pH 7.4
  • TA 70
  • CH 350
  • Water °F 85

Worked by hand: Mustard: 60% of CYA = 36 ppm, held 24 hours. +31 ppm × 15,000 gal ÷ 781.8 = 595 fl oz = 4.6 gal, rounded to 4¾.

Sources: T6, T9Spec §2 mustard algae shock; §3 SLAM

Worked answer and engine result for case 16
CheckWorked answerEngine todayResult
Statusurgenturgent
StepsSLAM, retestSLAM, retest
Dose: SLAM4¾ gal4¾ gal
SLAM FC3636
Engine and independent reference for case 16
Cross-checkEngineRef.Result
10% liquid chlorine, FC 5 to 364.65 gal4.52 gal2.8% more, by design
Mustard shock level at CYA 6036 ppm34 ppmdifferent formula, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).
  • Mustard algae level: we shock mustard algae at 60% of CYA, the more cautious published level; the reference uses CYA ÷ 2 + 4.5. Ours must equal the chart value worked by hand.

Salt pools

17

Salt pool, CYA 80, chlorine under the minimum

19,150-gallon salt cell pool, plaster

  • FC 3.5
  • CC 0
  • CYA 80
  • pH 7.8
  • TA 70
  • CH 440
  • Salt 3200
  • Water °F 90

Worked by hand: Chlorine: +3.5 ppm × 19,150 gal ÷ 781.8 (10% liquid) = 85.7 fl oz, about 11 cups. Acid: pH 7.8 to 7.5 at TA 70 = 13.6 fl oz of 31.45%.

Sources: T4, T5, LSpec §2 SWG minimum; §5 pH; §6 liquid chlorine

Worked answer and engine result for case 17
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepslower pH, raise FC, salt cell output, retestlower pH, raise FC, salt cell output, retest
Dose: raise FC11 cups11 cups
Dose: lower pH1¾ cups1¾ cups
FC minimum44
FC target min66
FC target max1111
FC shock level3131
Engine and independent reference for case 17
Cross-checkEngineRef.Result
31.45% acid, pH 7.8 to 7.5 at TA 7013.6 fl oz13.6 fl ozSame
10% liquid chlorine, FC 3.5 to 785.7 fl oz83.4 fl oz2.8% more, by design
Salt pool FC minimum at CYA 804 ppm4 ppmSame
Top of the FC target at CYA 8011 ppm11 ppmSame
SLAM level at CYA 8031 ppm21 ppmdifferent formula, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).
  • SLAM level: our shock level follows the published FC/CYA chart (about 40% of CYA); the reference uses poolcalculator.com's own formula. Ours must equal the chart value worked by hand.

18

Salt 2,500: top up to 3,200

20,000-gallon salt cell pool, plaster

  • FC 6
  • CC 0
  • CYA 70
  • pH 7.6
  • TA 70
  • CH 350
  • Salt 2500
  • Water °F 84

Worked by hand: k = 7,468.6. +700 ppm × 20,000 gal ÷ 7,468.6 = 1,875 oz = 117 lb, rounded to 115 lb (3 bags).

Sources: T24, LSpec §6 salt; §8 salt

Worked answer and engine result for case 18
CheckWorked answerEngine todayResult
Statusactact
Stepsadd salt, retestadd salt, retest
Dose: add salt115 lb115 lb
Engine and independent reference for case 18
Cross-checkEngineRef.Result
Salt, 2,500 to 3,200 ppm117.2 lb117.2 lbSame

19

Salt pool with FC 13: turn the cell down

20,000-gallon salt cell pool, plaster

  • FC 13
  • CC 0
  • CYA 70
  • pH 7.6
  • TA 70
  • CH 350
  • Salt 3300
  • Water °F 84

Worked by hand: SWG at CYA 70: minimum floor(0.045 × 70 + 0.7) = 3, target up to floor(70/10 + 3.5) = 10. FC 13 is above the band but below SLAM, so lower the output 10%.

Sources: T4, T5, T6, LSpec §2 FC vs CYA (SWG); §9 SWG output

Worked answer and engine result for case 19
CheckWorked answerEngine todayResult
Statusokok
Stepssalt cell output, retestsalt cell output, retest
FC minimum33
FC target min55
FC target max1010
Engine and independent reference for case 19
Cross-checkEngineRef.Result
Salt pool FC minimum at CYA 703 ppm3 ppmSame
Top of the FC target at CYA 7010 ppm10 ppmSame
SLAM level at CYA 7028 ppm20 ppmdifferent formula, by design
  • SLAM level: our shock level follows the published FC/CYA chart (about 40% of CYA); the reference uses poolcalculator.com's own formula. Ours must equal the chart value worked by hand.

20

New salt pool: chlorine, stabilizer and salt from zero

10,000-gallon salt cell pool, plaster

  • FC 0
  • CC 0
  • CYA 0
  • pH 7.6
  • TA 80
  • CH 300
  • Salt 0
  • Water °F 75

Worked by hand: Stabilizer: 70 × 10,000 ÷ 7,489.5 = 93.5 oz = 5.8 lb. Salt: 3,200 × 10,000 ÷ 7,468.6 = 4,285 oz = 268 lb, rounded to 270. Chlorine first: +3 ppm × 10,000 ÷ 781.8 = 38 fl oz.

Sources: T4, T24, LSpec §4 CYA targets; §6 stabilizer and salt; §9 plan order

Worked answer and engine result for case 20
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepskeep out, raise FC, salt cell output, raise CYA, add salt, retestkeep out, raise FC, salt cell output, raise CYA, add salt, retest
Dose: raise FC5 cups5 cups
Dose: raise CYA5¾ lb5¾ lb
Dose: add salt270 lb270 lb
Engine and independent reference for case 20
Cross-checkEngineRef.Result
10% liquid chlorine, FC 0 to 338.4 fl oz37.3 fl oz2.8% more, by design
Stabilizer, CYA 0 to 705.84 lb5.84 lbSame
Salt, 0 to 3,200 ppm267.8 lb267.8 lbSame
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

21

Salt 4,800: only dilution brings it down

15,000-gallon salt cell pool, plaster

  • FC 6
  • CC 0
  • CYA 70
  • pH 7.6
  • TA 70
  • CH 350
  • Salt 4800
  • Water °F 84

Worked by hand: Replace 1 − 3,200/4,800 = 33.3% of 15,000 gal = 5,000 gal of salt-free water.

Sources: T22, T24, LSpec §4 partial drains; §8 salt

Worked answer and engine result for case 21
CheckWorked answerEngine todayResult
Statusactact
First steppartial drainpartial drain
Dose: partial drain5,000 gal5,000 gal
Engine and independent reference for case 21
Cross-checkEngineRef.Result
Water to replace, salt 4,800 to 3,20033.3%33.3%Same

pH and acid

22

pH 8.2 with alkalinity 120

15,000-gallon liquid chlorine pool, plaster

  • FC 6
  • CC 0
  • CYA 40
  • pH 8.2
  • TA 120
  • CH 350
  • Water °F 85

Worked by hand: High TA: take pH down to 7.2 with acid, then aerate; acid plus aeration lowers TA over days. Pool Math's formula gives 52.3 fl oz, which also removes about 14 ppm TA.

Sources: T13, T13c, LSpec §5 pH and TA; §7 pH dose formula

Worked answer and engine result for case 22
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepslower pH, adjust TA, retestlower pH, adjust TA, retest
Engine and independent reference for case 22
Cross-checkEngineRef.Result
31.45% acid, pH 8.2 to 7.2 at TA 12052.3 fl oz52.3 fl ozSame
TA drop from that acid-13.6 ppm-13.64 ppmSame

23

Salt pool reading 8.2, the top of the pH test

18,000-gallon salt cell pool, plaster

  • FC 6
  • CC 0
  • CYA 70
  • pH 8.2
  • TA 70
  • CH 400
  • Salt 3200
  • Water °F 88

Worked by hand: 8.2 is the top of the phenol red scale, so the real pH may be higher: dose for 8.2 to 7.5 (22.4 fl oz, 3 cups), add half, retest and repeat.

Sources: T4, T13, LSpec §5 pH 8.2 is urgent; §7 pH dose formula

Worked answer and engine result for case 23
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepslower pH, retestlower pH, retest
Dose: lower pH3 cups3 cups
Engine and independent reference for case 23
Cross-checkEngineRef.Result
31.45% acid, pH 8.2 to 7.5 at TA 7022.4 fl oz22.4 fl ozSame

24

Borates 50 nearly quadruple the acid

15,000-gallon liquid chlorine pool, plaster

  • FC 6
  • CC 0
  • CYA 40
  • pH 8
  • TA 80
  • CH 350
  • Borates 50
  • Water °F 84

Worked by hand: Borates buffer pH, so the formula's borate term adds acid: 52.3 fl oz with 50 ppm borates against about 14 fl oz without.

Sources: T13, LSpec §7 pH dose formula (borate term)

Worked answer and engine result for case 24
CheckWorked answerEngine todayResult
Statusactact
Stepslower pH, retestlower pH, retest
Dose: lower pH6½ cups6½ cups
Engine and independent reference for case 24
Cross-checkEngineRef.Result
31.45% acid, pH 8.0 to 7.6 at TA 80, borates 5052.3 fl oz52.3 fl ozSame
Same pH change with no borates12.7 fl oz12.7 fl ozSame

25

14.5% "safer" acid takes more than twice the volume

20,000-gallon liquid chlorine pool, plaster, 14.5% acid on the shelf

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.9
  • TA 90
  • CH 350
  • Water °F 84

Worked by hand: At full strength this is 15.0 fl oz. 14.5% acid is weaker and also lighter, so each cup holds less acid: it takes 2.34 times the volume, 35.2 fl oz, about 4½ cups.

Sources: T27, LSpec §6 muriatic acid (14.5%); §12 14.5% acid

Worked answer and engine result for case 25
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepslower pH, retestlower pH, retest
Dose: lower pH4½ cups4½ cups
Engine and independent reference for case 25
Cross-checkEngineRef.Result
14.5% acid, pH 7.9 to 7.6 at TA 9035.2 fl oz32.6 fl oz7.9% more, by design
  • Weaker acid: we correct for weaker acid also being lighter; the reference scales by the percent alone (allowed: 7 to 9% more).

Alkalinity

26

Alkalinity 40: baking soda before acid

15,000-gallon liquid chlorine pool, plaster

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.9
  • TA 40
  • CH 350
  • Water °F 82

Worked by hand: Raise TA first, a little above 70 so it lands near 70 after the acid: 33 × 15,000 ÷ 4,461.6 = 111 oz = 6.9 lb. Baking soda nudges pH to 7.97; acid to 7.6 at TA 73 is 11.1 fl oz.

Sources: T1, T13, LSpec §5 order and method; §6 baking soda

Worked answer and engine result for case 26
CheckWorked answerEngine todayResult
Statusactact
Stepsadjust TA, lower pH, retestadjust TA, lower pH, retest
Dose: adjust TA7 lb7 lb
Dose: lower pH1½ cups1½ cups
Engine and independent reference for case 26
Cross-checkEngineRef.Result
Baking soda, TA 40 to 736.93 lb6.93 lbSame
Then acid, pH 7.97 to 7.6 at TA 7311.1 fl oz11.1 fl ozSame

27

Alkalinity 45 with pH in range

20,000-gallon liquid chlorine pool, plaster

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.5
  • TA 45
  • CH 350
  • Water °F 82

Worked by hand: k = 4,461.6. +25 ppm × 20,000 gal ÷ 4,461.6 = 112 oz = 7.0 lb.

Sources: T1, T13, LSpec §5 TA; §6 baking soda

Worked answer and engine result for case 27
CheckWorked answerEngine todayResult
Statusactact
Stepsadjust TA, retestadjust TA, retest
Dose: adjust TA7 lb7 lb
Engine and independent reference for case 27
Cross-checkEngineRef.Result
Baking soda, TA 45 to 707 lb7 lbSame

28

Alkalinity 140: acid to 7.2, then aerate

15,000-gallon liquid chlorine pool, plaster

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.7
  • TA 140
  • CH 350
  • Water °F 82

Worked by hand: TA comes down by acid plus aeration: acid to pH 7.2 (46 fl oz, removing about 12 ppm TA), aerate back to 7.6, repeat daily.

Sources: T13, T13c, LSpec §5 lower TA; §7 pH dose formula

Worked answer and engine result for case 28
CheckWorked answerEngine todayResult
Statusactact
Stepsadjust TA, retestadjust TA, retest
Dose: adjust TA6 cups6 cups
Engine and independent reference for case 28
Cross-checkEngineRef.Result
31.45% acid, pH 7.7 to 7.2 at TA 14046.1 fl oz46.1 fl ozSame
TA drop per round-12 ppm-12.03 ppmSame

Calcium and saturation (CSI)

29

Vinyl pool with low calcium is fine

18,000-gallon liquid chlorine pool, vinyl

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 150
  • Water °F 80

Worked by hand: Vinyl needs little calcium: CH 50 to 550 is acceptable, so no calcium step. CSI −0.30 is inside the ±0.6 vinyl band.

Sources: T1, T3, T11Spec §7 CSI bands; §8 calcium by surface

Worked answer and engine result for case 29
CheckWorked answerEngine todayResult
Statusokok
Stepsnothing to addnothing to add
CSI-0.30-0.30
Engine and independent reference for case 29
Cross-checkEngineRef.Result
CSI-0.30-0.30Same

30

Plaster pool with calcium 140

20,000-gallon liquid chlorine pool, plaster

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 140
  • Water °F 82

Worked by hand: k = 6,754.1 × 0.94 = 6,348.9. +210 ppm × 20,000 gal ÷ 6,348.9 = 662 oz = 41.3 lb, added in portions.

Sources: T3, T12, LSpec §6 calcium chloride; §8 calcium by surface

Worked answer and engine result for case 30
CheckWorked answerEngine todayResult
Statusactact
Stepsraise calcium, retestraise calcium, retest
Dose: raise calcium41 lb41 lb
Engine and independent reference for case 30
Cross-checkEngineRef.Result
Calcium chloride (94%), CH 140 to 35041.3 lb38.9 lb6.4% more, by design
  • Calcium chloride purity: we dose for 94% pellets; the reference assumes pure calcium chloride (allowed: 6 to 7% more).

31

Calcium flakes (77%) need more than pellets

12,000-gallon liquid chlorine pool, plaster, calcium flakes on the shelf

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 120
  • Water °F 82

Worked by hand: Flakes are dihydrate: k = 5,098.8 × 0.77 ÷ 0.755 = 5,200. +230 ppm × 12,000 gal ÷ 5,200 = 531 oz = 33.2 lb.

Sources: T12, LSpec §6 calcium chloride (flakes)

Worked answer and engine result for case 31
CheckWorked answerEngine todayResult
Statusactact
Stepsraise calcium, retestraise calcium, retest
Dose: raise calcium33 lb33 lb
Engine and independent reference for case 31
Cross-checkEngineRef.Result
Calcium chloride flakes, CH 120 to 35033.2 lb33.8 lb1.9% less, by design
  • Calcium chloride flakes: we dose for flakes labelled 77%; the reference uses pure dihydrate at 75.5% (allowed: 1.5 to 2.5% less).

32

Calcium 1,100: replace water in two rounds

15,000-gallon liquid chlorine pool, plaster

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 1100
  • Water °F 82

Worked by hand: Replace 1 − 350/1,100 = 68.2% (10,227 gal). More than half at once is unsafe, so 2 rounds of 1 − (350/1,100)^½ = 43.6% each.

Sources: T3, T22, LSpec §4 partial drains in rounds; §8 calcium

Worked answer and engine result for case 32
CheckWorked answerEngine todayResult
Statusactact
First steppartial drainpartial drain
Dose: partial drain10,200 gal10,200 gal
Engine and independent reference for case 32
Cross-checkEngineRef.Result
Water to replace, CH 1,100 to 35068.2%68.2%Same
Each of 2 rounds43.6%43.6%Same

33

Cold plaster pool with low calcium: corrosive

15,000-gallon liquid chlorine pool, plaster

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.3
  • TA 60
  • CH 150
  • Water °F 65

Worked by hand: CSI = pH − 11.677 + log CH + log carbonate alkalinity − ionic term − 1412.5/(T + 273.15) + 4.7375, about −0.8 at 65 °F: below −0.6 on plaster, so raise calcium.

Sources: T11, T31, LSpec §7 CSI; §8 calcium

Worked answer and engine result for case 33
CheckWorked answerEngine todayResult
Statusactact
Stepsraise calcium, retestraise calcium, retest
CSI-0.80-0.80
Engine and independent reference for case 33
Cross-checkEngineRef.Result
CSI-0.80-0.80Same

34

Hot salt pool with high calcium: scale-forming

15,000-gallon salt cell pool, plaster

  • FC 6
  • CC 0
  • CYA 70
  • pH 7.8
  • TA 90
  • CH 600
  • Salt 3400
  • Water °F 92

Worked by hand: CSI +0.38 at 92 °F with CH 600 and salt 3,400: above +0.3 on plaster. Lowering pH to 7.5 is the quickest way back.

Sources: T4, T11, T31, LSpec §7 CSI bands

Worked answer and engine result for case 34
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepslower pH, retestlower pH, retest
CSI+0.38+0.38
Engine and independent reference for case 34
Cross-checkEngineRef.Result
CSI+0.38+0.38Same
31.45% acid, pH 7.8 to 7.5 at TA 9013.2 fl oz13.2 fl ozSame

35

Same water, different surface: vinyl only needs watching

15,000-gallon liquid chlorine pool, vinyl

  • FC 6
  • CC 0
  • CYA 40
  • pH 7.4
  • TA 60
  • CH 100
  • Water °F 72

Worked by hand: CSI −0.79 would be act on plaster (beyond −0.6) but is watch on vinyl (−0.6 to −1.0). The Taylor-method LSI for the dashboard is −0.86.

Sources: T11, T31, TY3, LSpec §7 CSI bands by surface; LSI (Taylor)

Worked answer and engine result for case 35
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsnothing to addnothing to add
CSI-0.79-0.79
LSI-0.86-0.86
Engine and independent reference for case 35
Cross-checkEngineRef.Result
CSI-0.79-0.79Same

Stabilizer and partial drains

36

Tablet pool with CYA creep to 90

20,000-gallon tablets (trichlor) pool, plaster

  • FC 5
  • CC 0
  • CYA 90
  • pH 7.5
  • TA 90
  • CH 350
  • Water °F 85

Worked by hand: Replace 1 − 40/90 = 55.6% of 20,000 gal = 11,111 gal, rounded to 11,100, in 2 rounds of 33.3%.

Sources: T3, T5b, T22Spec §4 CYA targets and partial drains; §9 stop the source

Worked answer and engine result for case 36
CheckWorked answerEngine todayResult
Stepsswitch sanitizer, partial drain, raise FC, retestswitch sanitizer, partial drain, raise FC, retest
Dose: partial drain11,100 gal11,100 gal
Engine and independent reference for case 36
Cross-checkEngineRef.Result
Water to replace, CYA 90 to 4055.6%55.6%Same
Each of 2 rounds33.3%33.3%Same

37

CYA 10: stabilizer, then chlorine for the new CYA

15,000-gallon liquid chlorine pool, plaster

  • FC 3
  • CC 0
  • CYA 10
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 82

Worked by hand: +30 ppm × 15,000 gal ÷ 7,489.5 = 60 oz = 3.8 lb. Dose chlorine as if the CYA is already 40: +3 ppm = 57.6 fl oz, about 7 cups.

Sources: T14, T23, LSpec §4 raising CYA; §6 stabilizer

Worked answer and engine result for case 37
CheckWorked answerEngine todayResult
Statusactact
Stepsraise CYA, raise FC, retestraise CYA, raise FC, retest
Dose: raise CYA3¾ lb3¾ lb
Dose: raise FC7 cups7 cups
Engine and independent reference for case 37
Cross-checkEngineRef.Result
Stabilizer, CYA 10 to 403.76 lb3.76 lbSame
10% liquid chlorine for CYA 40, FC 3 to 657.6 fl oz56 fl oz2.8% more, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

38

CYA 120: replace two thirds of the water in two rounds

16,000-gallon liquid chlorine pool, plaster

  • FC 10
  • CC 0
  • CYA 120
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 82

Worked by hand: Replace 1 − 40/120 = 66.7% (10,667 gal) in 2 rounds of 1 − (1/3)^½ = 42.3%. The refill dilutes FC 10 to 3.3; bring it back to 6 for CYA 40.

Sources: T3, T22, LSpec §4 partial drains in rounds

Worked answer and engine result for case 38
CheckWorked answerEngine todayResult
Statusactact
Stepspartial drain, raise FC, retestpartial drain, raise FC, retest
Dose: partial drain10,700 gal10,700 gal
Engine and independent reference for case 38
Cross-checkEngineRef.Result
Water to replace, CYA 120 to 4066.7%66.7%Same
Each of 2 rounds42.3%42.3%Same
10% liquid chlorine after the refill, FC 3.3 to 655.3 fl oz53.8 fl oz2.8% more, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

39

Vinyl pool at CYA 200: three rounds

20,000-gallon liquid chlorine pool, vinyl

  • FC 12
  • CC 0
  • CYA 200
  • pH 7.6
  • TA 70
  • CH 200
  • Water °F 82

Worked by hand: Replace 1 − 40/200 = 80% (16,000 gal). Rounds of at most half need 3: 1 − 0.2^(1/3) = 41.5% each, keeping 12 to 18 in of water over the liner.

Sources: T22, LSpec §4 partial drains in rounds (vinyl)

Worked answer and engine result for case 39
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepspartial drain, raise FC, retestpartial drain, raise FC, retest
Dose: partial drain16,000 gal16,000 gal
Engine and independent reference for case 39
Cross-checkEngineRef.Result
Water to replace, CYA 200 to 4080%80%Same
Each of 3 rounds41.5%41.5%Same

Hot tubs

40

Bromine hot tub, bromine 2

400-gallon bromine hot tub, acrylic

  • FC 1
  • Bromine 2
  • pH 7.6
  • TA 70
  • CH 150
  • Water °F 102

Worked by hand: Spa bromine target 4 to 6 ppm; an FC reading is ignored in a bromine tub. Balance (CSI −0.02) is fine.

Sources: T16, T11Spec §8 bromine

Worked answer and engine result for case 40
CheckWorked answerEngine todayResult
Statusactact
Stepsraise bromine, retestraise bromine, retest
CSI-0.02-0.02
Engine and independent reference for case 40
Cross-checkEngineRef.Result
CSI-0.02-0.02Same

41

300-gallon hot tub: tablespoons, not cups

300-gallon liquid chlorine hot tub, acrylic

  • FC 1
  • CC 0
  • CYA 30
  • pH 7.5
  • TA 60
  • CH 150
  • Water °F 100

Worked by hand: Spa CYA 30: target 4 to 6, ideal 5. +4 ppm × 1,136 L ÷ 100 g/L = 45 mL, about 1½ fl oz (3 tbsp).

Sources: T5, T17Spec §8 hot tubs; §10 practical amounts

Worked answer and engine result for case 41
CheckWorked answerEngine todayResult
Dose: raise FC1½ fl oz1½ fl oz
Engine and independent reference for case 41
Cross-checkEngineRef.Result
10% liquid chlorine, FC 1 to 51.53 fl oz1.49 fl oz2.8% more, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

42

Hot tub with CYA 10: dichlor builds it up

400-gallon dichlor hot tub, acrylic

  • FC 1
  • CC 0
  • CYA 10
  • pH 7.5
  • TA 60
  • CH 150
  • Water °F 100

Worked by hand: +3 ppm × 400 gal ÷ 4,149 = 0.29 oz (about 8 g), adding 2.7 ppm CYA. Keep using dichlor until CYA reaches 20 to 40.

Sources: T15, T30, LSpec §4 hot tub CYA; §6 dichlor

Worked answer and engine result for case 42
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepsraise CYA, raise FC, retestraise CYA, raise FC, retest
Dose: raise FC¼ oz¼ oz
Engine and independent reference for case 42
Cross-checkEngineRef.Result
Dichlor, FC 1 to 40.29 oz0.29 ozSame
CYA added by that dose2.73 ppm2.73 ppmSame

43

Hot tub with CC 0.7: shock to 12

350-gallon liquid chlorine hot tub, acrylic

  • FC 2
  • CC 0.7
  • CYA 30
  • pH 7.5
  • TA 60
  • CH 150
  • Water °F 102

Worked by hand: Spa SLAM at CYA 30 is 12 ("shock to 12 ppm"). +10 ppm × 350 gal ÷ 781.8 = 4.5 fl oz, rounded to 4.

Sources: T15, T9, LSpec §8 hot tubs; §2 SLAM level

Worked answer and engine result for case 43
CheckWorked answerEngine todayResult
Statusurgenturgent
StepsSLAM, retestSLAM, retest
Dose: SLAM4 fl oz4 fl oz
SLAM FC1212
Engine and independent reference for case 43
Cross-checkEngineRef.Result
10% liquid chlorine, FC 2 to 124.48 fl oz4.36 fl oz2.8% more, by design
SLAM level at CYA 3012 ppm13 ppmdifferent formula, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).
  • SLAM level: our shock level follows the published FC/CYA chart (about 40% of CYA); the reference uses poolcalculator.com's own formula. Ours must equal the chart value worked by hand.

44

Bromine hot tub at pH 8.0

400-gallon bromine hot tub, acrylic

  • Bromine 5
  • pH 8
  • TA 80
  • CH 150
  • Water °F 102

Worked by hand: Acid dosing is the same whatever the sanitizer: pH 8.0 to 7.5 at TA 80 in 400 gal = 0.45 fl oz, about 2½ tsp.

Sources: T16, T17, LSpec §5 pH (spa); §7 pH dose formula

Worked answer and engine result for case 44
CheckWorked answerEngine todayResult
Statusactact
Stepslower pH, retestlower pH, retest
Dose: lower pH2½ tsp2½ tsp
Engine and independent reference for case 44
Cross-checkEngineRef.Result
31.45% acid, pH 8.0 to 7.5 at TA 800.45 fl oz0.45 fl ozSame

45

Hot tub with alkalinity 30

300-gallon liquid chlorine hot tub, acrylic

  • FC 5
  • CC 0
  • CYA 30
  • pH 7.4
  • TA 30
  • CH 150
  • Water °F 100

Worked by hand: Hot tub TA goal 60: +30 ppm × 300 gal ÷ 4,461.6 = 2.0 oz.

Sources: T17, LSpec §5 TA (hot tub); §6 baking soda

Worked answer and engine result for case 45
CheckWorked answerEngine todayResult
Statusactact
Stepsadjust TA, retestadjust TA, retest
Dose: adjust TA2 oz2 oz
Engine and independent reference for case 45
Cross-checkEngineRef.Result
Baking soda, TA 30 to 602.02 oz2.02 ozSame

Metric units

46

Metric: 56,781 L pool, doses in litres

15,000-gallon liquid chlorine pool, plaster, metric doses

  • FC 3.5
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 82

Worked by hand: 1,420 mL of 10% liquid chlorine, rounded to the nearest 0.25 L.

Sources: LSpec §6 liquid chlorine; §10 metric amounts

Worked answer and engine result for case 46
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepsraise FC, retestraise FC, retest
Dose: raise FC1.5 L1.5 L
Engine and independent reference for case 46
Cross-checkEngineRef.Result
10% liquid chlorine, FC 3.5 to 61,419 mL1,380 mL2.8% more, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

47

50,000 L pool with 12.5% liquid chlorine

50,000-litre liquid chlorine pool, plaster, metric doses, 12.5% chlorine on the shelf

  • FC 2
  • CC 0
  • CYA 40
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 82

Worked by hand: 12.5% liquid chlorine holds about 125 g of chlorine per litre: +4 ppm × 50,000 L = 200 g, so 1.6 L, rounded to 1.5 L.

Sources: T25, LSpec §6 liquid chlorine (trade %); §10 metric amounts

Worked answer and engine result for case 47
CheckWorked answerEngine todayResult
Statusurgenturgent
Stepsraise FC, retestraise FC, retest
Dose: raise FC1.5 L1.5 L
Engine and independent reference for case 47
Cross-checkEngineRef.Result
12.5% liquid chlorine, FC 2 to 61,598 mL1,555 mL2.7% more, by design
  • Chlorine strength: we follow Pool Math's strength table for chlorine; the reference scales in a straight line with the label percent (allowed: up to 3% apart).

48

40,000 L salt pool: salt in kilograms

40,000-litre salt cell pool, plaster, metric doses

  • FC 6
  • CC 0
  • CYA 70
  • pH 7.6
  • TA 70
  • CH 350
  • Salt 2400
  • Water °F 82

Worked by hand: +800 ppm (mg/L) × 40,000 L = 32 kg of salt: one 20-kg bag and a bit over half another.

Sources: T24, LSpec §6 salt; §10 metric amounts

Worked answer and engine result for case 48
CheckWorked answerEngine todayResult
Statusactact
Stepsadd salt, retestadd salt, retest
Dose: add salt32 kg32 kg
Engine and independent reference for case 48
Cross-checkEngineRef.Result
Salt, 2,400 to 3,200 ppm32.1 kg32.1 kgSame

49

1,500 L hot tub: acid in millilitres

1,500-litre liquid chlorine hot tub, acrylic, metric doses

  • FC 5
  • CC 0
  • CYA 30
  • pH 7.9
  • TA 80
  • CH 150
  • Water °F 100

Worked by hand: pH 7.9 to 7.5 at TA 80 in 396 gal: 0.39 fl oz = 11.5 mL, rounded to 10 mL (add half, retest).

Sources: T17, LSpec §7 pH dose formula; §10 metric amounts

Worked answer and engine result for case 49
CheckWorked answerEngine todayResult
Statuswatchwatch
Stepslower pH, retestlower pH, retest
Dose: lower pH10 mL10 mL
Engine and independent reference for case 49
Cross-checkEngineRef.Result
31.45% acid, pH 7.9 to 7.5 at TA 8011.5 mL11.5 mLSame

50

20,000 L pool: stabiliser in grams

20,000-litre liquid chlorine pool, plaster, metric doses

  • FC 5
  • CC 0
  • CYA 20
  • pH 7.6
  • TA 70
  • CH 350
  • Water °F 82

Worked by hand: +20 ppm (mg/L) × 20,000 L = 400 g of cyanuric acid.

Sources: T14, LSpec §6 stabilizer; §10 metric amounts

Worked answer and engine result for case 50
CheckWorked answerEngine todayResult
Stepsraise CYA, retestraise CYA, retest
Dose: raise CYA400 g400 g
Engine and independent reference for case 50
Cross-checkEngineRef.Result
Stabiliser, CYA 20 to 40400 g400 gSame

Sources

Archived copies, so each citation can be checked as it was read.

Try the engine yourself: the water check and the free tools run the same code.