PoolDose Pool shock calculator: how much shock to add
Shocking a pool is a normal chlorine dose with a high target. Multiply the ppm you want to add by the volume in cubic metres, then divide by the strength on the label. For 10,000 gallons going from 0 to 10 ppm, that is 85.3 fl oz of 15% liquid or 1.23 lb of calcium hypochlorite.
What does the app do for shock?
PoolDose has a Shock dose row on the Dosing screen, under Shock level (SLAM), worked out from your CYA reading. You can also type your own high target in Target (ppm). The maths is grams of active chlorine, which is ppm times cubic metres, divided by the fraction of chlorine in the product: 0.15, 0.10, 0.68, 0.90 or 0.56.
What the app adds is a small helper at the bottom of the screen for choosing that target, described below. Volume in gallons is divided by 264.172052 to get cubic metres, and results are shown in fluid ounces, gallons, ounces or pounds.
Pool volume and chlorine dose
- Distance between bends
- Shrink
- Multiplier
Enter numbers of zero or more; the set or the roll must be above zero.
Showing the worked example. Turn on JavaScript to calculate your own numbers.
Volume = area × average depth (sloped bottom: shallow + deep ÷ 2; kidney = 0.85 × length × width × depth). Active chlorine in grams = (target − now) ppm × m³; product = active ÷ label strength. The target is the number you type: use your local rule or your test kit. It ignores chlorine lost to sun and demand, so treat it as a starting dose and re-test.
How much shock for 0 to 10 ppm in gallons?
| Chlorine source | 1,000 gal | 10,000 gal | 20,000 gal | 30,000 gal |
|---|---|---|---|---|
| Liquid sodium hypochlorite, 15% | 8.5 fl oz | 85.3 fl oz | 1.33 gal | 2.00 gal |
| Liquid sodium hypochlorite, 10% | 12.8 fl oz | 1.00 gal | 2.00 gal | 3.00 gal |
| Calcium hypochlorite, 65-70% | 2.0 oz | 1.23 lb | 2.45 lb | 3.68 lb |
| Trichlor, 90% | 1.5 oz | 14.8 oz | 1.85 lb | 2.78 lb |
| Dichlor, 56% | 2.4 oz | 1.49 lb | 2.98 lb | 4.47 lb |
The result is linear. Half the rise is half the dose: for 5 ppm on 10,000 gallons with 15% liquid, take half of 85.3 fl oz. If your jug carries another strength, such as 12.5%, scale the 15% line by 15 divided by your percentage.
And in litres and cubic metres?
| Chlorine source | 10 m³ | 20 m³ | 30 m³ | 50 m³ |
|---|---|---|---|---|
| Liquid sodium hypochlorite, 15% | 667 ml | 1.33 l | 2.00 l | 3.33 l |
| Liquid sodium hypochlorite, 10% | 1.00 l | 2.00 l | 3.00 l | 5.00 l |
| Calcium hypochlorite, 65-70% | 147 g | 294 g | 441 g | 735 g |
| Trichlor, 90% | 111 g | 222 g | 333 g | 556 g |
| Dichlor, 56% | 179 g | 357 g | 536 g | 893 g |
A pool of 10 m³ holds 10,000 litres, so the same table answers a litres question: 667 ml of 15% liquid shock per 10,000 litres for 10 ppm.
How do I get these numbers in PoolDose?
- Open Calculator > Volume and tap Use this volume, or type the volume into the volume field on Dosing. In Settings > Units choose US to enter gallons.
- Open Dosing and keep Product on Chlorine.
- Under Chlorine source, pick the product you own.
- Enter your strip reading in Measured (ppm) and the shock level in Target (ppm).
- Read the amount under Dose.
What is the shock level helper?
Below Dose, a section called Shock level (SLAM) asks for Your CYA (ppm), your stabilizer reading. It then shows a Shock target (ppm) of about 40% of that figure, never below 10 ppm free chlorine, then a Shock dose, the amount of your chosen product to get from your Measured (ppm) reading up to that target, and Use as target copies the target into the dose calculation.
| Your CYA (ppm) | Shock target (ppm) |
|---|---|
| 20 | 10 |
| 25 | 10 |
| 30 | 12 |
| 40 | 16 |
| 50 | 20 |
| 60 | 24 |
Take a 30 m³ pool with a CYA of 50 and a strip reading of 2 ppm. The helper proposes 20 ppm, so the rise is 18 ppm, which is 3.60 l of 15% liquid or 794 g of calcium hypochlorite.
The helper only suggests a target and a dose. It does not run a full SLAM, does not count days and does not know when the water is clear. The footer reminds you to keep the level there until the water holds it overnight.
What the number does not know
- It assumes the label percentage is available chlorine and ignores chlorine demand, sunlight and chlorine already bound up, so the real rise can be lower.
- It does not model what the product leaves behind: trichlor and dichlor add stabilizer, calcium hypochlorite adds hardness.
- The app does not judge algae or cloudy water. It only does the dosing sum.