40,000 gallon pool: how much of each chemical
A 40,000-gallon pool needs about 41 fl oz of 12.5% liquid chlorine to raise free chlorine (FC) by 1 ppm.
Always follow your product’s label directions. Pool and spa chlorine, bromine, shock and algaecides are EPA-registered pesticides: use products labeled for pool or spa use, and don’t swim or soak until levels are within the limit on your product’s label. If this page and a label disagree, the label wins.
| Product | +1 ppm FC | +2 ppm FC | +5 ppm FC | +10 ppm FC |
|---|---|---|---|---|
| Pool liquid chlorine 12.5% | 41 fl oz1.21 L | 82 fl oz2.42 L | 1.6 gal (205 fl oz)6.06 L | 3.2 gal (410 fl oz)12.11 L |
| Pool liquid chlorine 10% | 51 fl oz1.51 L | 102 fl oz3.03 L | 2.0 gal (256 fl oz)7.57 L | 4.0 gal (512 fl oz)15.14 L |
| Household bleach 6% | 82 fl oz2.44 L | 1.3 gal (165 fl oz)4.88 L | 3.2 gal (412 fl oz)12.19 L | 6.45 gal (824 fl oz)24.38 L |
| Household bleach 8.25% | 58 fl oz1.72 L | 116 fl oz3.43 L | 2.25 gal (290 fl oz)8.58 L | 4.55 gal (580 fl oz)17.15 L |
| Cal-hypo 65% | 8.2 oz233 g | 1.05 lb466 g | 2.55 lb1.16 kg | 5.15 lb2.33 kg |
| Dichlor 56% | 9.5 oz270 g | 1.2 lb541 g | 3.0 lb1.35 kg | 5.95 lb2.70 kg |
| Trichlor 90% | 5.9 oz168 g | 11.9 oz336 g | 1.85 lb841 g | 3.7 lb1.68 kg |
Liquid chlorine percent is the trade percent on pool chlorine jugs; bleach percent is by weight. Cal-hypo adds calcium. Dichlor and trichlor add stabilizer (CYA). To shock, follow the directions on your product’s label.
| Product | Change | Amount |
|---|---|---|
| Baking soda | TA +10 ppm | 5.6 lb2.54 kg |
| Muriatic acid 31.45% | TA −10 ppm | 102 fl oz3.03 L |
| Dry acid 93.2% | TA −10 ppm | 8.55 lb3.89 kg |
| Muriatic acid 31.45% | pH 7.8 → 7.5 (TA 100, CYA 40) | 38 fl oz1.13 L |
| Dry acid 93.2% | pH 7.8 → 7.5 (TA 100, CYA 40) | 3.2 lb1.46 kg |
| Soda ash | pH 7.2 → 7.5 (TA 80, CYA 30) | 3.7 lb1.68 kg |
pH doses depend on your TA and CYA, so use the calculator for your numbers. Acid and pH-up amounts are rounded down.
| Product | Change | Amount |
|---|---|---|
| Stabilizer (CYA) | +10 ppm | 3.35 lb1.51 kg |
| Stabilizer (CYA) | 0 → 40 ppm (new fill) | 13.4 lb6.06 kg |
| Calcium chloride 77% | CH +10 ppm | 4.8 lb2.18 kg |
| Calcium chloride 77% | CH +50 ppm (one step) | 24.0 lb10.90 kg |
| Pool salt | 0 → 3,200 ppm (new fill) | 1,068 lb484.53 kg · 27 × 40 lb bags |
| Pool salt | +500 ppm | 167 lb75.71 kg |
On this page (10 sections)
With 10% chlorine, it takes 51 fl oz, and with 6% bleach, 82 fl oz. At this size, a gallon of 12.5% adds only about 3.1 ppm, so you buy chlorine several jugs at a time, and a salt pool needs salt in large quantities.
Quick answer: chlorine for a 40,000 gallon pool (depends on product)
From FC 1 to 4 ppm, add about 123 fl oz of 12.5% liquid chlorine (just under a gallon), 1.2 gallons of 10%, or 1.95 gallons of 6% bleach. Dry equivalents are about 1.55 lb of 65% cal-hypo or 1.1 lb of 90% trichlor. With stabilizer (CYA) at 40 ppm, keep FC at 3–5 ppm.
Weekly use is the number to plan around. A pool that loses 1 ppm a day uses about 2.25 gallons of 12.5% chlorine a week; at 2 ppm a day, about 4.5 gallons. One gallon of 10% adds 2.5 ppm, so a single 10% jug covers only about a day and a quarter of a 2 ppm loss.
Dose table: chlorine by product for +1/+2/+5/+10 ppm
At +5 ppm the liquid doses are 1.6 gallons of 12.5% and 2 gallons of 10%; at +10 ppm, 3.2 and 4 gallons. Dry products per 1 ppm are about 8.2 oz of cal-hypo, 9.5 oz of dichlor, and 5.9 oz of trichlor. The liquid chlorine calculator corrects for strength lost in storage, which matters more when you buy in bulk.
Buying in bulk without wasting chlorine
Liquid chlorine loses strength while it sits. According to PHTA, 12.5% sodium hypochlorite loses half its strength in about 180 days at 77 °F and in about 48 days at 95 °F. A month's supply for a 2 ppm-a-day pool is about 18 gallons; in a hot garage, the last jugs will be noticeably weaker than the first. Buy one to two weeks at a time in summer, store jugs in the shade with caps closed, and use the oldest first. To check a jug's real strength, compare the rise a dose should give with a retest. The liquid chlorine calculator shows how.
Shock: four times the label's 10,000-gallon dose
Your shock product's label gives the dose. This pool holds four times the 10,000 gallons most labels are written for, so multiply the printed amount by 4. With liquid chlorine and a label that says 1 gallon per 10,000 gallons, that is 4 gallons. Aged jugs are weaker than the percent on the label, so use your freshest ones for a shock.
A 1 lb bag of 65% cal-hypo adds under 2 ppm of chlorine here (about 1.9 ppm) and about 1.4 ppm of calcium. A label that calls for 1 lb per 10,000 gallons means 4 lb, so count your bags before you start. Stay out of the water until chlorine is back at or below the label's swim limit, often 4 ppm. Guide: how to shock a pool.
pH and alkalinity: acid and baking soda
For pH 7.8 to 7.5 when total alkalinity (TA) is 100 and CYA is 40, add about 38 fl oz of 31.45% muriatic acid or 3.2 lb of dry acid. The same change takes about 32 fl oz at TA 80 and 44 fl oz at TA 120.
- Lower TA by 10 ppm: about 102 fl oz of muriatic acid, 0.8 gallon.
- Raise TA by 10 ppm: about 5.6 lb of baking soda; a +30 ppm step is about 16.8 lb (baking soda in a pool).
- Raise pH 7.2 to 7.5 (TA 80, CYA 30): about 3.7 lb of soda ash.
Pour acid slowly along the deep end in front of a return with the pump running. For your readings: muriatic acid calculator.
Stabilizer, calcium, and salt
- Stabilizer: 3.35 lb per 10 ppm; 13.4 lb from 0 to 40 ppm; about 23.4 lb from 0 to 70 ppm for a salt pool. It dissolves slowly, so add it in portions and retest after several days. See the stabilizer calculator.
- Calcium chloride (77%): 4.8 lb per 10 ppm; 24 lb for a +50 ppm step. Pre-dissolve it in buckets of pool water, a few pounds at a time.
- Salt: about 1,068 lb from 0 to 3,200 ppm, more than half a ton. Each 40 lb bag adds about 120 ppm; 26 bags reach about 3,115 ppm and the 27th reaches the target. See the pool salt calculator.
Pools that hold about 40,000 gallons
No above-ground pool in our model list comes near this volume. Inground estimates from length × width × average depth × 7.48:
| Size | Depth, shallow → deep | Gallons |
|---|---|---|
| 20 × 45 ft | 3.5 → 8.5 ft | 40,395 |
| 22 × 44 ft | 3.5 → 7.5 ft | 39,826 |
| 25 × 45 ft | 3.5 → 5.5 ft | 37,870 |
Hoppers, steps, and benches move the real number by several percent, so a measured fill or a salt-rise check gives a better volume than a tape measure. Circulation is slow as well: at 60 gallons per minute, one turnover of 40,000 gallons takes about 11 hours (pump run time calculator).
Calculator preset to this volume
The calculator above is set to 40,000 gallons. Enter your volume and test results; it gives doses in gallons and pounds and splits large acid doses into steps. Smaller sheet: 30,000 gallons; all sizes: dosing.
Safety. Storing chemicals in bulk adds risk: keep chlorine and acid in separate, ventilated places, never stacked together. The CDC estimates pool chemical injuries led to 4,535 U.S. emergency department visits a year (2008–2017). Never mix chemicals, add them at least 30 minutes apart, and wear gloves and eye protection. Always follow the product label. Poison Control: 1-800-222-1222.
FAQ
How much chlorine do I put in a 40,000 gallon pool?
About 41 fl oz of 12.5% liquid chlorine, 51 fl oz of 10%, or 82 fl oz of 6% bleach per 1 ppm. From FC 1 to 4, just under a gallon of 12.5%. See how much chlorine to add.
How much shock for a 40,000 gallon pool?
Four times the "per 10,000 gallons" amount on your shock label. If the label says 1 lb of cal-hypo per 10,000 gallons, use 4 lb; if it says 1 gallon of liquid chlorine, use 4 gallons. Don't swim until chlorine drops to the label's swim limit.
How much muriatic acid for a 40,000 gallon pool?
About 38 fl oz of 31.45% acid for pH 7.8 to 7.5 at TA 100 and CYA 40, and about 0.8 gallon to lower TA by 10 ppm.
Sources
- PHTA fact sheet, Sodium hypochlorite (strength loss in storage): phta.org
- CDC, Pool chemical injuries press release, May 16, 2019: cdc.gov
- Hayward, How much salt to add: hayward.com
- Formulas and reference checks: methodology