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).
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 current cyanuric acid level in parts per million. Check your most recent test strip, test kit, or pool store water test result. Enter 0 if your pool is unstabilized or you have not added stabilizer.
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 drops to 5 ppm or below 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 to kill algae, bacteria, and combined chlorine (the stuff that makes your pool smell). This calculator tells you the exact amount of shock product to add based on your pool size, stabilizer level, and current chlorine reading. Just enter your pool volume in gallons, your cyanuric acid (stabilizer) level in ppm, your current free chlorine reading, and the type of shock you plan to use. The calculator will return the Target Chlorine Level (Shock Point), Chlorine Increase Needed, and the exact Product to Add by weight or liquid volume—no guesswork.
Shocking works because the calculator uses industry-standard breakpoint chlorination: your target chlorine must reach 40 percent of your stabilizer level to actually kill contaminants. The formula accounts for your current chlorine so you only add what you need.
This calculator works in four steps. First, it calculates your Target Chlorine Level (Shock Point) by multiplying your CYA (stabilizer) level by 0.4—that's the breakpoint threshold where chlorine becomes effective. If your CYA is zero, the calculator sets a minimum target of 10 ppm. Second, it finds the Chlorine Increase Needed by subtracting your current chlorine from the target. Third, it converts that ppm increase into Pure Chlorine Required in pounds using the pool chemistry constant: 1 ppm in 10,000 gallons equals 0.0834 pounds of pure chlorine. Fourth, it divides by the available chlorine percentage in your chosen product type—cal-hypo granules are typically 65–73 percent available chlorine, while liquid chlorine is 10–12.5 percent—to give you the exact Product to Add by weight or fluid volume.
The calculator also warns you if you choose dichlor shock, which adds stabilizer to your pool as a side effect (shown as Stabilizer Added by This Treatment).
📐How it's calculated▼
The formula starts by finding your target shock level using breakpoint chlorination. Breakpoint chlorination is the point where chlorine kills all the bad stuff in your water. The formula is: Target Chlorine Level (Shock Point) = CYA × 0.4. So if your pool stabilizer is 60 ppm, your target is 60 × 0.4 = 24 ppm. That's the chlorine level you need to reach.
Next, you find how much chlorine you actually need to add: Chlorine Increase Needed = Target Level − Current Level. If your pool is at 3 ppm chlorine right now, you need to raise it by 24 − 3 = 21 ppm.
Then you convert that ppm number into actual pounds of pure chlorine using this relationship: for every 10,000 gallons of water, 1 ppm of chlorine equals 0.0834 pounds. Finally, you divide the pure chlorine weight by the strength of your shock product. Cal-hypo granules are 65 percent pure chlorine, so you divide by 0.65 to get the actual product weight.
Worked example: You have a 15,000-gallon pool with 60 ppm CYA and 3 ppm current chlorine. You buy 65 percent cal-hypo. Target = 60 × 0.4 = 24 ppm. Increase needed = 24 − 3 = 21 ppm. Pure chlorine = 21 × (15,000 ÷ 10,000) × 0.0834 = 21 × 1.5 × 0.0834 = 2.63 pounds pure chlorine. Product weight = 2.63 ÷ 0.65 = 4.05 pounds of granular shock to add.
📎Source: Pool & Hot Tub Alliance (PHTA)
🔍Finding your inputs▼
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): Enter your current cyanuric acid level in parts per million. Check your most recent test strip or pool store water test result. If you have never added stabilizer or your pool is outdoors and exposed to sunlight without stabilizer, enter 0. Even if you do not know the exact number, your pool store can test it for free.
Current Chlorine Level (ppm): Enter your pool's current free chlorine level in parts per million, measured with a test kit or test strip. Use the free chlorine number, not total chlorine. If your chlorine is completely gone, enter 0. Test strips can give a range, so estimate the middle number.
Shock Product Type: Select the specific type of shock you plan to buy. Cal-hypo is the most common granular shock (powder). Choose 65 percent or 73 percent based on the bag label. Dichlor is another granular option. Liquid chlorine is a clear liquid that looks like bleach and comes in 1-gallon jugs or larger—choose 12.5 percent or 10 percent based on the jug label.
⚠️Special situations▼
CYA level is zero (unstabilized pool)
The calculator sets a minimum Target Chlorine Level (Shock Point) of 10 ppm. You still need to shock, but your target is just 10 ppm instead of a percentage of stabilizer. This is standard practice for outdoor pools without stabilizer or indoor pools.
CYA is above 100 ppm
Your target chlorine would be over 40 ppm, which is unsafe for swimming and wastes shock product. Drain 25–50 percent of your pool and refill with fresh water to lower CYA first, then shock. Do not add more shock into high-CYA water.
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. Test again in a few days to see if chlorine drops before shocking.
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. If you use dichlor repeatedly, your CYA will climb and eventually require a partial drain. Use cal-hypo or liquid chlorine for routine shocking instead.
You are adding more than 5 pounds of granular shock at once
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. Make sure your pump is running during and for at least 8 hours after shock.
Your liquid chlorine jug is old (over 6 months)
Liquid chlorine loses strength over time in storage and sunlight. The available chlorine percentage on the label may be higher than what is actually in the jug. Buy fresh product when possible, or add slightly more than the calculator recommends and retest in 12 hours.
You want to return to the pool soon after shocking
Maximum safe chlorine for swimming is 5 ppm according to health department standards. Shock at night and test chlorine the next morning before anyone swims. If chlorine is still above 5 ppm, wait longer and retest.
❓Common questions▼
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 can build up over time. Liquid chlorine (sodium hypochlorite solution) is a clear liquid very similar to household bleach but at higher strength. It does not add stabilizer and dissolves instantly, so it works fast. Liquid chlorine costs more per gallon but requires less product weight. Use cal-hypo for routine shocking, dichlor only if you have low stabilizer and want to add it simultaneously, and liquid chlorine if you prefer fast dissolution and have easy access to it.
Why do I need to know my CYA (stabilizer) level to shock my pool?
CYA (cyanuric acid) is a chemical that protects chlorine from the sun's UV rays. But CYA also makes chlorine less reactive, so you need more chlorine in the water to kill algae and bacteria—this is breakpoint chlorination. The higher your CYA, the higher your target chlorine must be. For example, at 30 ppm CYA your target is 12 ppm chlorine, but at 80 ppm CYA your target jumps to 32 ppm. If you ignore CYA and just use a generic shock dose, you might add too little or way too much. That is why this calculator asks for it.
What happens if my CYA gets too high?
If CYA climbs above 100 ppm, your target shock level becomes impractically high (over 40 ppm), and no amount of chlorine will reliably kill algae. This problem is called CYA lock. The only fix is to drain 25–50 percent of your pool water and refill it with fresh water. This dilutes the CYA. You cannot remove CYA by adding chemicals. Prevention is easier than cure: use cal-hypo for routine shocking (does not add CYA), and avoid using dichlor repeatedly. Check your CYA level once per year and do a partial drain if it exceeds 100 ppm.
How do I measure my current free chlorine level accurately?
Use a liquid test kit with DPD (diethyl-p-phenylenediamine) reagent or an FAS-DPD test kit. These are the most accurate. Test strips are simpler but less precise. Never use an old test kit—the reagents expire and give false readings. Buy a new kit each season. Take the water sample from 12 inches below the surface (not the top), away from the pump intake and the jets. Test in shade or indoors. Write down the free chlorine reading, not total chlorine. If you are unsure, bring a sample to your pool store and ask them to test it for free. Their meter is usually very accurate.
Can I shock my pool during the day, or must I wait until night?
You can shock any time, but night is best because chlorine is not burned off by the sun. Shocking at night also prevents dangerously high chlorine levels from irritating your skin or eyes if someone enters the pool too soon. If you must shock during the day, do it late afternoon and run your pump for 12 hours, then test chlorine before anyone swims. The safest chlorine level for swimming is 2–5 ppm. If your pool has very warm water or high bather load, shock in the evening and test in the morning before opening the pool.