PooloraHow much chlorine powder to add to a pool
Most chlorine powder and bagged "shock" is one of two chemicals: calcium hypochlorite (cal-hypo) or dichlor. Here is how much of each for your pool size, in ounces and pounds, and what else it leaves in the water.
- 10,000 gallons, +1 ppm free chlorine: about 2 oz (60 g) of 65% cal-hypo.
- Shock from 2 to 10 ppm in 10,000 gallons: 1 lb (16 oz · 465 g) of 65% cal-hypo.
- Cal-hypo adds calcium; dichlor adds stabilizer, about 9 ppm for every 10 ppm of chlorine.
Which powder do you have?
Look for the active ingredient and the "available chlorine" percentage on the label:
- Calcium hypochlorite (cal-hypo): usually 65% or 73% available chlorine. Most bagged "shock" is this.
- Sodium dichloro-s-triazinetrione (dichlor): usually 56% or 62%. It is stabilized chlorine, so it adds cyanuric acid.
- Trichloro-s-triazinetrione (trichlor): about 90%, almost always sold as tablets for a floater or feeder, not for dosing by hand.
Use the chart that matches your percentage. A higher percentage simply means less product for the same result.
Chart: cal-hypo 65%
| Pool size | +1 ppm | +2 ppm | +3 ppm | Shock 2 → 10 ppm |
|---|---|---|---|---|
| 5,000 gal | 1 oz 30 g | 2 oz 60 g | 3 oz 85 g | 8 oz 235 g |
| 10,000 gal | 2 oz 60 g | 4 oz 115 g | 6 oz 175 g | 1 lb 465 g |
| 15,000 gal | 3 oz 85 g | 6 oz 175 g | 9 oz 260 g | 1.5 lb 700 g |
| 20,000 gal | 4 oz 115 g | 8 oz 235 g | 12.5 oz 350 g | 2.1 lb 930 g |
| 25,000 gal | 5 oz 145 g | 10.5 oz 290 g | 15.5 oz 435 g | 2.6 lb 1.15 kg |
| 30,000 gal | 6 oz 175 g | 12.5 oz 350 g | 1.2 lb 525 g | 3.1 lb 1.4 kg |
Chart: cal-hypo 73%
| Pool size | +1 ppm | +2 ppm | +3 ppm | Shock 2 → 10 ppm |
|---|---|---|---|---|
| 5,000 gal | 1 oz 25 g | 2 oz 50 g | 2.5 oz 80 g | 7.5 oz 205 g |
| 10,000 gal | 2 oz 50 g | 3.5 oz 105 g | 5.5 oz 155 g | 14.5 oz 415 g |
| 15,000 gal | 2.5 oz 80 g | 5.5 oz 155 g | 8 oz 235 g | 1.4 lb 620 g |
| 20,000 gal | 3.5 oz 105 g | 7.5 oz 205 g | 11 oz 310 g | 1.8 lb 830 g |
| 25,000 gal | 4.5 oz 130 g | 9 oz 260 g | 13.5 oz 390 g | 2.3 lb 1.05 kg |
| 30,000 gal | 5.5 oz 155 g | 11 oz 310 g | 1 lb 465 g | 2.7 lb 1.25 kg |
Chart: dichlor 56% and 62%
| Pool size | 56% +1 ppm | 56% +3 ppm | 62% +1 ppm | 62% +3 ppm |
|---|---|---|---|---|
| 5,000 gal | 1 oz 35 g | 3.5 oz 100 g | 1 oz 30 g | 3 oz 90 g |
| 10,000 gal | 2.5 oz 70 g | 7 oz 205 g | 2 oz 60 g | 6.5 oz 185 g |
| 15,000 gal | 3.5 oz 100 g | 10.5 oz 305 g | 3 oz 90 g | 9.5 oz 275 g |
| 20,000 gal | 5 oz 135 g | 14.5 oz 405 g | 4.5 oz 120 g | 13 oz 365 g |
| 25,000 gal | 6 oz 170 g | 1.1 lb 505 g | 5.5 oz 155 g | 1 lb 460 g |
| 30,000 gal | 7 oz 205 g | 1.3 lb 610 g | 6.5 oz 185 g | 1.2 lb 550 g |
There is no shock column for dichlor on purpose: going from 2 to 10 ppm with dichlor also adds about 7.3 ppm of stabilizer, every time. For shocking, cal-hypo or liquid chlorine leave no stabilizer behind.
What each one adds to your water
- Cal-hypo adds about 7 ppm of calcium hardness for every 10 ppm of chlorine. Useful in a plaster pool that is low on calcium; with hard fill water or frequent shocks, calcium keeps climbing and can scale. It adds no stabilizer.
- Dichlor adds about 9 ppm of stabilizer (CYA) for every 10 ppm of chlorine. Handy to build stabilizer in a fresh fill, but used every day it pushes CYA past 50 ppm within weeks, and then the pool needs more chlorine to stay clean. See the stabilizer guide.
- Trichlor tablets add about 6 ppm of CYA for every 10 ppm of chlorine and pull pH and alkalinity down.
What a 1 lb bag really does
Many bags say one pound treats 10,000 gallons. In 10,000 gallons, 1 lb of 65% cal-hypo raises free chlorine by about 7.8 ppm (and calcium by 5.5 ppm). One pound of 56% dichlor raises it by about 6.7 ppm and adds 6.1 ppm of stabilizer. Whether that is enough depends on your stabilizer: how to shock a pool shows the level to aim for.
How to add it
- Pre-dissolve cal-hypo in a bucket of pool water (powder into water, never water onto powder), let it settle a minute and pour the liquid in front of a return with the pump running. Undissolved granules can bleach vinyl liners and spot plaster.
- Dichlor dissolves quickly; on vinyl liners pre-dissolve it too.
- Add it in the evening: sunlight burns off chlorine fast, especially with little stabilizer.
- Never mix cal-hypo with trichlor tablets or any other chemical, and never store them together: they can react violently and even start a fire.
- Keep everyone out until a test shows free chlorine back within your label's swimming range.
Common questions
Is pool shock the same as chlorine?
Most shock is chlorine (cal-hypo or dichlor) sold in a single-dose bag. "Non-chlorine shock" (potassium monopersulfate) is a different product: it oxidizes, but it does not raise free chlorine or disinfect.
Cal-hypo or liquid chlorine?
Both raise free chlorine. Liquid chlorine leaves only a little salt behind; cal-hypo stores longer and is easier to carry, but adds calcium. Compare the cost of reaching the same ppm, not the price per bag.
How much cal-hypo for a 20,000-gallon pool?
To raise free chlorine 2 ppm: about 8 oz (235 g) of 65% cal-hypo. To shock from 2 to 10 ppm: about 2.1 lb (33 oz · 930 g).
Do it with your own products
Poolora turns your test into the exact amount of the products on your shelf, in cups and ounces, in the right order, and tells you when it's safe to swim. Free to start; every chemical, water balance and history are part of Pro.
Keep going
Sources
- Product labels and safety data sheets for calcium hypochlorite, dichlor and trichlor (available chlorine; do not mix with other chemicals)
- Pool & Hot Tub Alliance (PHTA): alkalinity fact sheet (tablets lower pH and alkalinity)
- Doses and side effects: Poolora engine (mass balance with the stoichiometry of each product)