Pool Shock Treatment Calculator
Calculate exactly how much pool shock or bleach you need. Supports HTH, calcium hypochlorite, and liquid chlorine for any pool size (e.g. 12,000 gallons).
Shocking for an event? You're in the right place. Just topping your chlorine back up to its normal everyday level is regular dosing, not shocking: use the Chlorine Dosing Calculator →
Routine shock is the regular maintenance dose — weekly upkeep, after heavy swimming, or after a storm. Choose algae cleanup when the water is green or cloudy with visible growth: killing a bloom takes a much higher chlorine level that scales with your stabilizer, held until the water clears.
Total volume of your pool in US gallons. Check your pool builder paperwork or use a pool volume calculator based on shape and dimensions.
Your pool's current free chlorine reading in parts per million. Use a DPD or FAS-DPD test kit for accuracy. Enter 0 if chlorine is completely depleted.
Select the type of shock product you plan to use. Cal-hypo is the most common granular shock. Liquid chlorine is sodium hypochlorite solution, the same as household bleach but stronger.
Shock Treatment Results
Safety Reminder
Shock your pool at dusk or night. Wait until free chlorine returns to the 1–3 ppm safe range before allowing swimmers. Pre-dissolve granular shock in a bucket of pool water before adding. Never mix chemicals.
💡About this calculator▼
Shocking your pool means adding a large dose of chlorine all at once — but how large depends entirely on why you're shocking, and that's the question this calculator asks first. Routine shock — the weekly upkeep dose, or the reset after a pool party or a storm — raises your free chlorine to 10 ppm, which for a typical pool works out to the familiar one pound of cal-hypo per 10,000 gallons. Algae cleanup is a different animal: killing a green or cloudy bloom takes a far higher chlorine level that scales with your stabilizer reading, held until the water clears.
Pick your purpose, enter your pool volume and current chlorine reading (plus your stabilizer level for algae jobs), choose your product, and the calculator returns the target chlorine level, the increase needed, and the exact amount of product to add by weight or liquid volume — no guesswork, and no algae-strength doses for a Tuesday-night maintenance shock.
One boundary keeps this page honest: shocking is a spike, not a lifestyle. Your pool's everyday chlorine level is a different, lower number that scales with your stabilizer — about 3–5 ppm free chlorine at 30 ppm CYA, 7–9 at 80 — and keeping it there between shocks is the job of our chlorine dosing calculator, linked below.
The calculator sets a different chlorine target for each purpose, then converts the gap into product.
Routine shock targets 10 ppm free chlorine — the standard breakpoint convention for maintenance shocking. From a typical starting point of 2 ppm, that reproduces the industry-standard dose of about one pound of 65% cal-hypo per 10,000 gallons, which is exactly what most shock bag labels tell you. Your stabilizer level isn't needed for this dose.
Algae cleanup (SLAM) targets 40 percent of your stabilizer (CYA) level — at CYA 50 that's 20 ppm, at CYA 80 it's 32 ppm — with a floor of 10 ppm for unstabilized pools. The dose must scale with CYA because stabilizer buffers chlorine's killing power: the more CYA in the water, the more chlorine it takes to reach the concentration that actually kills a bloom. Critically, algae cleanup is a held process, not a single dose — you retest every few hours, re-dose to stay at the target, and finish only when the pool loses less than 1 ppm of chlorine overnight.
From the target, the math is the same either way: the increase needed (target minus current chlorine) converts to pure chlorine at 0.0834 pounds per 10,000 gallons per ppm, then divides by your product's available-chlorine strength — cal-hypo at 65–73 percent, dichlor at 56 percent, liquid chlorine at 10–12.5 percent — to give the exact weight or volume to add. Dichlor users also see how much stabilizer the treatment adds as a side effect.
📐How it's calculated▼
Routine shock: Target = 10 ppm. From your current reading, Increase Needed = 10 − Current Level. Worked example: a 15,000-gallon pool at 2 ppm needs an 8 ppm rise. Pure chlorine = 8 × 1.5 × 0.0834 = 1.0 pound — about 1.5 pounds of 65% cal-hypo (1.0 ÷ 0.65), matching the label convention of a pound per 10,000 gallons.
Algae cleanup: Target = CYA × 0.4 (minimum 10 ppm, CYA capped at 100). Worked example: the same 15,000-gallon pool with 60 ppm CYA at 3 ppm chlorine. Target = 60 × 0.4 = 24 ppm. Increase = 21 ppm. Pure chlorine = 21 × 1.5 × 0.0834 = 2.63 pounds — about 4 pounds of 65% cal-hypo, added in stages and held at the target until the water clears and overnight chlorine loss falls under 1 ppm.
The conversion constants: 1 ppm in 10,000 gallons equals 0.0834 pounds of pure chlorine; product weight = pure chlorine ÷ available-chlorine fraction (cal-hypo 0.65 or 0.73, dichlor 0.56); liquid chlorine delivers its trade percentage × 0.08346 pounds of chlorine per gallon (12.5% ≈ 1.04 lbs/gal).
📎Sources:PoolChemTracker — FC/CYA Chart (algae/SLAM level = 40% of CYA; hold until overnight chlorine loss < 1 ppm),Swim University — How to Shock a Pool (standard routine dose: 1 lb cal-hypo per 10,000 gallons; weekly cadence; 1–3 ppm swim-safe range),In The Swim — Ultimate Guide to Pool Chlorine (available-chlorine % by product)
🔍Finding your inputs▼
What are you shocking for?: This choice sets the entire dose. Routine shock covers scheduled upkeep and recovery after heavy use, rain, or hot spells — the maintenance dose. Algae cleanup is for water that's visibly going wrong: green tint, cloudy haze, slippery walls. If you can see algae, choose algae cleanup — an under-dosed bloom recovers and you'll have spent the chlorine for nothing.
Pool Size (gallons): Enter the total volume of your pool in US gallons. Check your pool paperwork, measure the pool dimensions and use an online pool volume calculator, or ask your pool builder.
Stabilizer (CYA) Level (ppm) — algae cleanup only: Enter your current cyanuric acid level in parts per million. Check your most recent test strip or pool store water test result. The kill level scales with CYA, so this number matters most when it's high. Enter 0 if your pool is unstabilized; if you don't know it, your pool store can test it for free.
Current Chlorine Level (ppm): Enter your pool's current free chlorine level, measured with a test kit or strip. Use the free chlorine number, not total chlorine. If chlorine is completely gone, enter 0. For algae cleanup at high targets, a FAS-DPD drop kit is the only reliable way to read the elevated levels.
Shock Product Type: Select the product you plan to use. Cal-hypo is the most common granular shock. Liquid chlorine is sodium hypochlorite solution — the same chemical as household bleach but stronger. Dichlor works but adds stabilizer with every dose.
⚠️Special situations▼
CYA level is zero (unstabilized pool)
Both modes converge at a 10 ppm target: routine shock always targets 10, and the algae kill level floors at 10 when there is no stabilizer buffering the chlorine. This is standard for indoor pools and freshly filled outdoor pools. Note that an outdoor pool without CYA burns off chlorine fast in sunlight — shock at dusk so the dose works overnight instead of evaporating in the afternoon sun.
CYA is above 100 ppm
Your algae-cleanup target would be over 40 ppm, which is unsafe for swimming and wastes shock product. The calculator caps the math at CYA 100, but the real fix is water: drain 25–50 percent of your pool and refill, then retest and shock. You cannot remove CYA with chemicals. Routine shocks at very high CYA are also weakened — the 10 ppm dose does less than it would in balanced water, which is another argument for the partial drain.
Current chlorine is already at or above target level
The calculator shows Chlorine Increase Needed of 0 ppm and Product to Add of 0 pounds. You do not need to shock. For an algae cleanup, "at target" is the goal state, not the finish line — stay there with retesting until the water clears and overnight chlorine loss is under 1 ppm. For a routine shock, test again in a few days.
You choose dichlor shock product
Dichlor adds stabilizer to your pool at a rate of about 0.9 ppm CYA for every 1 ppm of free chlorine you add — the calculator shows this as Stabilizer Added by This Treatment. One algae cleanup with dichlor at a 20 ppm target adds roughly 18 ppm of CYA, which then raises every future algae target. Use cal-hypo or liquid chlorine for shocking; save dichlor for pools that genuinely need more stabilizer.
You are adding a large granular dose
Do not dump all the shock in one spot. Pre-dissolve the granules in a bucket of pool water first, stir until dissolved, then pour the solution around the pool perimeter. Never add more than 5 pounds of granular shock per 10,000 gallons in a single dose — split large algae-cleanup doses into stages. Keep the pump running during and for at least 8 hours after.
❓Common questions▼
How much shock do I need for routine weekly shocking?
Enough to raise your free chlorine to 10 ppm — for a typical pool sitting at 2 ppm, that works out to about one pound of 65% cal-hypo per 10,000 gallons, the same standard dose printed on most shock bags. This calculator sharpens that label dose by accounting for your actual current chlorine: if your pool is already at 5 ppm, you need half the product the label assumes. Shock weekly or at least every other week in swim season, at dusk, with the pump running.
Why is the algae dose so much bigger than a normal shock?
Because killing an established bloom takes a fundamentally higher chlorine concentration than maintenance cleaning — and because stabilizer (CYA) buffers chlorine, the kill level scales with your CYA reading: 40 percent of it, so 20 ppm at CYA 50 and 32 ppm at CYA 80. An algae treatment that doesn't reach and hold that level is counterproductive: the bloom recovers, and you've spent the chlorine for nothing. That's also why algae cleanup is a held process with retesting, not a single dose.
What is the difference between cal-hypo, dichlor, and liquid chlorine shock?
Cal-hypo (calcium hypochlorite) is a white granular powder that is the most affordable and most common shock type. It does not add stabilizer to your pool. Dichlor (sodium dichloroisocyanurate) is a granular powder that kills algae fast but adds stabilizer as a side effect, which builds up over time. Liquid chlorine (sodium hypochlorite solution) is a clear liquid very similar to household bleach but at higher strength — no stabilizer added, dissolves instantly. Use cal-hypo or liquid chlorine for shocking; use dichlor only if you also want to raise stabilizer.
Why do I need to know my CYA (stabilizer) level to treat algae?
CYA (cyanuric acid) protects chlorine from the sun's UV rays, but it also makes chlorine less aggressive — so the more CYA in your water, the higher your chlorine must go to reach algae-killing strength. At 30 ppm CYA the kill level is 12 ppm chlorine; at 80 ppm CYA it jumps to 32 ppm. Ignore CYA and use a generic dose, and you'll either underdose (the bloom recovers) or overdose (wasted product). Routine maintenance shocks don't need the CYA number — the 10 ppm target covers normal upkeep.
What is CYA lock and how do I fix it?
If CYA climbs above roughly 100 ppm, your algae-kill target becomes impractically high (over 40 ppm) and no reasonable amount of chlorine reliably clears a bloom. The only fix is dilution: drain 25–50 percent of the pool and refill with fresh water — no chemical removes CYA. Prevention is easier: shock with cal-hypo or liquid chlorine (neither adds CYA), avoid repeated dichlor or trichlor use, and test CYA at least yearly.
When can I swim after shocking the pool?
When free chlorine returns to the 1–3 ppm safe range — test before anyone gets in, and never judge by clock time alone. A routine 10 ppm shock at dusk is often swimmable the next day; an algae cleanup at 20–32 ppm takes longer, and you should hold the level until the water clears anyway. Sunlight burns chlorine down fastest in unstabilized pools, slowest in high-CYA water.
What should my chlorine level be day to day, between shocks?
Lower than anything on this page — and it scales with your stabilizer. The everyday operating bands: at 20 ppm CYA keep free chlorine at 2–4 ppm, at 30 CYA keep 3–5, at 50 CYA keep 5–7, and at 80 CYA keep 7–9 (roughly a minimum of 7.5 percent of your CYA). After any shock, chlorine naturally drifts back down toward that band. Maintaining it there is regular chlorine dosing, not shocking — our chlorine dosing calculator, linked below, suggests your band from your CYA and converts the top-up into product amounts.
🔗 Related Calculators
Chlorine Dosing Calculator
Calculate exactly how much chlorine to add to your pool. Enter your pool volume, current and target free chlorine levels, and chlorine product type to get the precise dose.
Cyanuric Acid Dosing Calculator
Calculate exactly how much cyanuric acid (pool stabilizer) to add to raise CYA to your target level — or how many gallons to drain if CYA is too high. Includes minimum free chlorine guidance.
Algaecide Dosing Calculator
Calculate exactly how much algaecide to add to your pool for weekly prevention, season opening, or an active bloom — with step-by-step guidance for treating green, yellow (mustard), and black algae. Enter your pool volume and algaecide type for the precise dose.
Pool Volume Calculator
Calculate your pool volume in gallons for rectangular, oval, round, and kidney-shaped pools. Enter length, width, and depth to get an accurate gallon count for chemical dosing.