Pool Shock Dosing Chart
A pool shock dosing chart: shock free chlorine targets by CYA, breakpoint chlorination doses by combined chlorine level, and how much 12.5% liquid chlorine or cal-hypo to add for pools from 5,000 to 40,000 gallons.
Quick answer: Shock to a free chlorine level of about 40 percent of your CYA, or add 10x your combined chlorine reading, whichever is higher. Per 10,000 gallons, every 1 ppm of FC takes about 10.7 fl oz of 12.5% liquid chlorine or 1.8 oz of 73% cal-hypo. A typical shock from 2 ppm up to a 16 ppm target in 10,000 gallons is about 150 fl oz (1.2 gallons) of liquid chlorine. Shock at dusk with the pump running and hold the level until combined chlorine is 0.5 ppm or less.
Safety first, every time. Never mix shock products or combine shock with any other chemical, especially acid or trichlor tablets, because the reaction can release toxic gas or cause a fire. Always add the chemical to the water, never water to the chemical. Pour liquid chlorine slowly around the deep end; pre-dissolve or broadcast cal-hypo per the label. Run the pump while dosing and retest before re-dosing. These figures are estimates from standard pool-care formulas, so test your own water and follow your product labels.
Shocking means raising free chlorine high enough to reach breakpoint chlorination, the point where chlorine destroys chloramines, algae, and bacteria instead of feeding them. There is no fixed cup-per-gallon shock dose: the right target scales with your cyanuric acid, and the amount of product scales with your pool volume. The tables below cover both. Confirm your gallons with the pool volume calculator, find your target, then read the dose. For an exact figure from your own test numbers, the shock calculator does the math for you.
Step 1: Find your shock FC target from CYA
The shock target is roughly 40 percent of your cyanuric acid reading. Higher stabilizer always needs higher chlorine. The full relationship, including minimum and everyday target levels, is in the FC/CYA chart.
| CYA (ppm) | Shock FC target (ppm) |
|---|---|
| 0 to 20 | 10 |
| 30 | 12 |
| 40 | 16 |
| 50 | 20 |
| 60 | 24 |
| 70 | 28 |
| 80 | 31 |
| 90 | 35 |
| 100 | 40 |
Subtract your current free chlorine from the target to get the ppm you need to add, then use the product tables below. If your CYA is above 80 to 100, shocking gets impractical; see how to lower CYA first.
Breakpoint dosing by combined chlorine level
When the problem is chloramines (a strong chlorine smell and red eyes with a combined chlorine reading above 0.5 ppm), the working rule is to add about 10 times your CC reading in free chlorine. This table shows that dose per 10,000 gallons; scale it to your pool size by simple multiplication.
| Combined chlorine (CC) | FC to add (10x rule) | Liquid chlorine 12.5% per 10,000 gal | Cal-hypo 73% per 10,000 gal |
|---|---|---|---|
| 0.5 ppm | 5 ppm | 54 fl oz | 9 oz |
| 1.0 ppm | 10 ppm | 107 fl oz (0.8 gal) | 18 oz (1.1 lb) |
| 1.5 ppm | 15 ppm | 160 fl oz (1.3 gal) | 27 oz (1.7 lb) |
| 2.0 ppm | 20 ppm | 214 fl oz (1.7 gal) | 36 oz (2.3 lb) |
| 3.0 ppm | 30 ppm | 321 fl oz (2.5 gal) | 54 oz (3.4 lb) |
If the 10x dose lands below the CYA-based shock target above, dose to the CYA target instead. Learn why chloramines form in free vs combined chlorine.
Liquid chlorine (12.5%) shock dosing chart
Fluid ounces of 12.5 percent sodium hypochlorite to raise free chlorine by the amount shown. One gallon is 128 fl oz. Liquid chlorine adds no CYA or calcium, which makes it the cleanest shock for most pools.
| Pool volume | Raise FC 10 ppm | Raise FC 15 ppm | Raise FC 20 ppm | Raise FC 25 ppm |
|---|---|---|---|---|
| 5,000 gal | 54 fl oz | 80 fl oz | 107 fl oz (0.8 gal) | 134 fl oz (1.0 gal) |
| 10,000 gal | 107 fl oz (0.8 gal) | 160 fl oz (1.3 gal) | 214 fl oz (1.7 gal) | 268 fl oz (2.1 gal) |
| 15,000 gal | 160 fl oz (1.3 gal) | 241 fl oz (1.9 gal) | 321 fl oz (2.5 gal) | 401 fl oz (3.1 gal) |
| 20,000 gal | 214 fl oz (1.7 gal) | 321 fl oz (2.5 gal) | 428 fl oz (3.3 gal) | 535 fl oz (4.2 gal) |
| 25,000 gal | 268 fl oz (2.1 gal) | 401 fl oz (3.1 gal) | 535 fl oz (4.2 gal) | 669 fl oz (5.2 gal) |
| 30,000 gal | 321 fl oz (2.5 gal) | 481 fl oz (3.8 gal) | 642 fl oz (5.0 gal) | 802 fl oz (6.3 gal) |
| 40,000 gal | 428 fl oz (3.3 gal) | 642 fl oz (5.0 gal) | 856 fl oz (6.7 gal) | 1,070 fl oz (8.4 gal) |
Using 10 percent liquid chlorine instead? Add about 25 percent more. Liquid chlorine also weakens with age and heat, so an old jug may need extra. For smaller 1 to 5 ppm adjustments, use the everyday chlorine dosing chart.
Cal-hypo (73%) shock dosing chart
Ounces by weight of 73 percent calcium hypochlorite. One pound is 16 ounces. For common 65 percent cal-hypo shock, multiply by about 1.12. Cal-hypo also raises calcium hardness, so go easy in hard-water pools.
| Pool volume | Raise FC 10 ppm | Raise FC 15 ppm | Raise FC 20 ppm | Raise FC 25 ppm |
|---|---|---|---|---|
| 5,000 gal | 9 oz | 13.5 oz | 18 oz (1.1 lb) | 22.5 oz (1.4 lb) |
| 10,000 gal | 18 oz (1.1 lb) | 27 oz (1.7 lb) | 36 oz (2.3 lb) | 45 oz (2.8 lb) |
| 15,000 gal | 27 oz (1.7 lb) | 40.5 oz (2.5 lb) | 54 oz (3.4 lb) | 67.5 oz (4.2 lb) |
| 20,000 gal | 36 oz (2.3 lb) | 54 oz (3.4 lb) | 72 oz (4.5 lb) | 90 oz (5.6 lb) |
| 25,000 gal | 45 oz (2.8 lb) | 67.5 oz (4.2 lb) | 90 oz (5.6 lb) | 112.5 oz (7.0 lb) |
| 30,000 gal | 54 oz (3.4 lb) | 81 oz (5.1 lb) | 108 oz (6.8 lb) | 135 oz (8.4 lb) |
| 40,000 gal | 72 oz (4.5 lb) | 108 oz (6.8 lb) | 144 oz (9.0 lb) | 180 oz (11.3 lb) |
Skip dichlor for shocking when you can: every 1 ppm of FC from dichlor adds about 0.9 ppm of CYA, which permanently raises the shock target for every future treatment.
Unstabilized shock products
CPDI Champion Liquid Pool Shock, 12.5% Sodium Hypochlorite
Pourable unstabilized chlorine; adds no CYA or calcium.
In The Swim Pool Shock 68% Cal-Hypo Granular (12 x 1 lb)
$49.99 on Amazon
Pre-measured one-pound bags of strong granular shock.
How to shock: the short version
- Test first. You need FC, CC, and CYA. A FAS-DPD kit reads free chlorine accurately up to shock levels; strips top out far below them.
- Dose at dusk. Sunlight destroys unprotected chlorine, so evening dosing lets the full dose work overnight.
- Run the pump. Circulate for at least several hours, ideally overnight, so the shock mixes through the whole pool.
- Hold the level. Retest and re-dose to maintain the shock FC until combined chlorine is 0.5 ppm or less, the water is clear, and chlorine holds overnight.
- Wait to swim. Test and confirm free chlorine is back in the normal range for your CYA before anyone gets in.
The full walkthrough, including product selection and what to do when the water will not clear, is in how to shock a pool. For a green pool, follow how to clear a green pool, which pairs this chart with filtering and brushing.
Dose to your test numbers, not to a bag label
Bag instructions like one pound per 10,000 gallons ignore both your CYA and your starting chlorine, which is why they so often underdose. Work the chart instead: target from CYA, subtract current FC, read the product amount for your gallons. The shock calculator runs those exact steps with your numbers, and the chemical dosing cheat sheet keeps every other dose one glance away. These figures are estimates from standard pool-care formulas, so always retest before adding more.
Frequently Asked Questions
How much shock do I need for a 10,000 gallon pool?
It depends on your CYA. At 40 ppm CYA the shock target is about 16 ppm free chlorine. If you are starting from 2 ppm FC, you need to add 14 ppm, which is about 150 fluid ounces (1.2 gallons) of 12.5 percent liquid chlorine or about 25 ounces (1.6 pounds) of 73 percent cal-hypo in 10,000 gallons. Find your target in the shock FC table, subtract your current free chlorine, and read the dose from the chart for your pool size.
What is the 10x rule for combined chlorine?
Breakpoint chlorination requires adding roughly 10 times your combined chlorine reading in free chlorine. If CC tests at 1.0 ppm, add about 10 ppm of FC; if CC is 2.0 ppm, add about 20 ppm. Falling short of breakpoint can actually create more chloramines, which is why a token half dose often makes the smell worse. When the 10x figure and the CYA-based shock target differ, dose to whichever is higher.
Can I shock a pool with dichlor?
You can, but it is usually a bad idea for routine shocking. Dichlor adds about 0.9 ppm of cyanuric acid for every 1 ppm of free chlorine, so a single 10 ppm shock adds roughly 9 ppm of CYA. A few dichlor shocks can push stabilizer high enough that every future shock needs far more chlorine, and the only way to lower CYA is a partial drain and refill. Use unstabilized liquid chlorine or cal-hypo for shocking instead.
How many bags of cal-hypo shock do I need?
Most granular shock is sold in 1 pound (16 ounce) bags. Take the ounces from the cal-hypo table and divide by 16. For example, raising free chlorine by 20 ppm in a 20,000 gallon pool takes about 72 ounces of 73 percent cal-hypo, which is 4.5 one-pound bags. If your product is 65 percent available chlorine instead of 73 percent, add about 12 percent more, so roughly 5 bags in that example.
How long do I hold the shock level?
Until three things are true: combined chlorine reads 0.5 ppm or less, the water is clear, and free chlorine holds overnight without a big drop. That can mean retesting and re-dosing several times a day for days during an algae bloom. Free chlorine falls as it destroys contaminants, so one dose almost never finishes the job. Test in the morning and at dusk, and keep the filter running the entire time.
How soon after shocking can I swim?
Wait until free chlorine falls back into the normal range for your CYA, typically 1 to 4 ppm for a low-CYA pool and somewhat higher for stabilized pools. That usually takes several hours to overnight after a routine shock and longer after a heavy algae treatment. Always test before anyone swims. Shock-level chlorine can irritate skin and eyes and bleach swimwear, so let the test kit clear the pool, not the clock.
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