Pool Shock Calculator
Pool Shock Calculator Determine precise pool shock dosage to reach target free chlorine using volume, ppm, product strength, and breakpoint chlorination calculations safely.
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Helping Notes
This tool mirrors TYOP’s shock workflow: enter pool gallons, current FC, CYA, choose SLAM or mustard, pick your product and strength.
SLAM shock level tracks CYA (≈40% of CYA). Mustard-algae shock uses ≈60% of CYA for a short 24-hour boost when needed.
Dichlor adds stabilizer (CYA). If your CYA is already high, prefer liquid chlorine or cal-hypo for shock dosing.
Results
Shock Target (ppm)
FC Increase Needed
Dose for Selected Product
What Is a Pool Shock Calculator?
A Pool Shock Calculator estimates how much chlorinating product you need to quickly raise free chlorine (FC) to a target level for sanitizing, oxidation, or clearing combined chlorine (chloramines). You enter pool volume, current FC and combined chlorine (CC), your desired shock level, and the product’s available chlorine percentage. The calculator converts between units, computes the required increase in parts per million (ppm), and translates that into a mass (or volume) of product. It also supports reverse calculations—predicting the FC increase from a chosen dose—so you can plan how many bags or jugs to buy. Using a calculator prevents underdosing (ineffective) and overdosing (wasteful, corrosive, or cloudy water), saving time and money while speeding recovery after heavy use, algae, or rain.
About the Pool Shock Calculator
The tool centers on two practical targets: breakpoint chlorination and problem clearing. Breakpoint chlorination raises FC to roughly ten times CC to oxidize chloramines efficiently. Problem clearing aims for a higher FC band based on cyanuric acid (CYA) stabilization. The engine uses your pool’s volume (directly entered or computed from dimensions) and the product’s available chlorine fraction to convert ppm goals into real-world masses. It supports granular products (e.g., calcium hypochlorite) and liquids (e.g., sodium hypochlorite). Optional helpers compute bag counts from package size and convert between mass and liquid volume using product density. Clear outputs include target FC, Δppm required, product mass, and predicted new FC—handy for scheduling filtration runtime and retesting.
Increase needed: ΔFCppm = max(0, FCtarget − FCcurrent)
Breakpoint target (rule of thumb): FCtarget,bp = 10 × CC
CYA-based target (generic): FCtarget ≈ kcya × CYA (0.3 ≤ kcya ≤ 0.5)
Mass as available chlorine (pounds): mCl₂,lb = Vgal · ΔFCppm · 8.34×10⁻⁶
Product required (pounds): mproduct,lb = mCl₂,lb / fac, where fac ∈ (0, 1] is available chlorine fraction.
Liquid volume from density: Vliq,L = mproduct,kg / ρkg/L
New FC after dosing: FCnew = FCcurrent + mCl₂,lb/(8.34×10⁻⁶·Vgal)
Volume from dimensions (rectangle): Vgal = LftWftDavg,ft × 7.48052
Round / oval pools: Vgal = π(Dft²/4)Davg,ft7.48052; Vgal = π(LftWft/4)Davg,ft7.48052
How to Use This Pool Shock Calculator
- Test water: record FC, CC, pH, and CYA. Choose a target—breakpoint (≈10×CC) or a CYA-based shock level.
- Enter pool volume (or compute from dimensions). Select your product’s available chlorine fraction and, if liquid, density.
- Submit to see Δppm required, product mass (lb/kg), optional liquid volume, and predicted new FC.
- Distribute product with the pump running; brush to aid mixing. Retest after thorough circulation and adjust if needed.
Examples
- 12,000 gal, FC 1, CC 1 (breakpoint): Target ≈ 10 ppm ⇒ ΔFC ≈ 9. mCl₂ ≈ 0.90 lb. Using 65% cal‑hypo: ≈ 1.38 lb.
- 15,000 gal, raise FC by 5 ppm with 12.5% liquid: mCl₂ ≈ 0.63 lb ⇒ product mass ≈ 5.04 lb (convert to volume using density).
- 10,000 gal algae clear target 20 ppm from FC 2: ΔFC = 18 ⇒ mCl₂ ≈ 1.50 lb.
- Reverse check: If you add 1.0 lb as Cl₂ to 13,000 gal: ΔFC ≈ 9.23 ppm.
Formula Snippets Ready for Rendering
FAQs
What is pool shocking and why do it?
Shocking rapidly raises free chlorine to oxidize contaminants, break down chloramines, and restore sanitizer effectiveness after heavy load or algae.
What ppm should I target when shocking?
For chloramine removal, aim near ten times CC. For algae or severe contamination, use a higher CYA‑based target.
Which product is best—cal‑hypo or liquid?
Cal‑hypo is strong and adds calcium; liquid works quickly and adds no stabilizer. Choose based on your water balance.
Can I use dichlor or trichlor for shocking?
Dichlor adds CYA and is sometimes used; trichlor dissolves slowly and is rarely ideal for rapid shock. Check your CYA level.
How long before swimming after shocking?
Wait until FC drops to your normal target range and pH is balanced. Always confirm with a reliable test.
My water turned cloudy after shock. Why?
High dosing can precipitate minerals or dead algae. Maintain filtration, brush, and clarify only if needed after retesting.
Does temperature or pH affect shock effectiveness?
Yes. Lower pH and warmer water increase hypochlorous acid proportion and speed. Keep pH in recommended range before shocking.
Should I shock at night?
Night or low‑sun periods minimize UV loss, making your dose more effective. Ensure the pump runs to circulate.
How do I avoid overshooting chlorine?
Measure accurately, dose in stages, and retest between additions. Use the calculator’s reverse check before adding more.
Can I shock a saltwater pool?
Yes. Use the same calculations. You may temporarily supplement the generator with liquid or granular chlorine for speed.
Do I need to adjust alkalinity or calcium before shocking?
Not specifically for the act of shocking, but balanced water reduces side effects like cloudiness or scaling afterward.
What test kit accuracy do I need?
Use a drop‑based kit capable of high‑range FC and CC readings. Strips are convenient but less precise for shock planning.
What if my CC stays high after shocking?
Repeat breakpoint dosing, maintain circulation and filtration, and investigate ammonia or organics that demand high chlorine.