Calcium hardness: how to raise it, and what to do if it's high

Doses checked 11/9/2026

Raise calcium hardness with calcium chloride. The official chart from the Indiana Department of Health gives 1.2 lb of calcium chloride 77% to raise it by 10 ppm in 10,000 US gallons. Plaster pools aim for 200–400 ppm; vinyl, fiberglass and painted pools 175–300 ppm. If calcium is too high, it can usually only be lowered by replacing some of the water: talk to a pool professional before draining.

Checked on every build: 17 tests of the sums this calculator runs, including 2 amounts printed in published charts, labels and manuals (ours must match them, or land under them where we start low on purpose) and 5 tests of its limits: caps, smaller rounds, and the cases where it gives no amount.

Read before you add anything

Never add acid and chlorine at the same time, and never mix them, even in a bucket or feeder. Mixing chlorine products with acid can create toxic gas. Add one, let the pump run, retest, then add the other.
Always add the chemical to water, never water to the chemical.
Add one chemical at a time. Never mix chemicals together, and use a separate clean scoop for each.
Add chemicals only when nobody is in the pool.
Wear the protective gear your product label asks for, such as goggles and gloves.
Handle chemicals in a well-ventilated area.
Add acid with the pump running, into the deep end, away from the skimmer and away from any floater or feeder that holds chlorine tablets.
Never add shock (cal-hypo or any other chlorine product) through the skimmer, or through any floater or feeder that holds or has held tablets, and never put different chlorine products in the same feeder.
Only pre-dissolve a chemical in a bucket if its label tells you to.
Store chemicals in a secure place away from children and pets, and never store liquid chemicals above dry chemicals.
Read the product label before each use. If the label differs from this estimate, follow the label.
These amounts are estimates. Add in stages and retest before adding more.
This tool cannot tell you the water is safe to swim in. Follow your product label, and if in doubt ask a pool professional.

Where each line comes from

CDC, Using Pool Chemicals Safely Official: “Never mix / Chlorine products with acid; this could create toxic gases” Source page (opens in a new browser tab)
12.5% liquid chlorine label, EPA-accepted Other source: “Mixing this product with chemicals (e.g. ammonia, acids, detergents, etc.) or organic matter (e.g. urine, feces, etc.)” ... “will release chlorine gas which is irritating to eyes, lungs and mucous membranes.” Source page (opens in a new browser tab)
CDC Official: “add pool chemical to water; NEVER add water to pool chemical” and “violent (potentially explosive) reaction can occur” Source page (opens in a new browser tab)
Virginia Department of Health Official: “Add chemicals to water - not water to chemicals.” Source page (opens in a new browser tab)
Indiana Department of Health Official: “Add acids to water, NEVER water to acid. Remember AAA (Always Add Acid).” Source page (opens in a new browser tab)
CDC Model Aquatic Health Code 2024, 5.9.3.4.2.3.1 Official: “Two or more chemicals shall never be mixed in the same dilution water.” Source page (opens in a new browser tab)
Indiana Official: “Never mix any chemicals together.” Source page (opens in a new browser tab)
Virginia Official: “Designate tools per chemical - Do not use the same scoop for different chemicals.” Source page (opens in a new browser tab)
MAHC 5.9.3.4.1.2 Official: “Chemicals added manually directly into the AQUATIC VENUE shall only be introduced in the absence of BATHERS.” Source page (opens in a new browser tab)
Virginia Official: “NEVER add pool chemicals when the pool is in use, and only add them poolside as directed by the product label.” Source page (opens in a new browser tab)
CDC, Using Pool Chemicals Safely Official: “Dress for safety by wearing appropriate safety equipment (for example, safety goggles, gloves, and mask)” Source page (opens in a new browser tab)
12.5% liquid chlorine label, EPA-accepted Other source: “Wear safety glasses or goggles and rubber gloves when handling this product.” Source page (opens in a new browser tab)
Alliance Trading pH Down (dry acid) label Other source: “Wear goggles or safety glasses and rubber gloves when handling this product.” Source page (opens in a new browser tab)
CDC, Using Pool Chemicals Safely Official: “Handle in a well-ventilated area” Source page (opens in a new browser tab)
Leslie's muriatic acid Other source: “With the pump running, pour the solution into the deep end of your pool, or away from the skimmer or any fixtures.” Source page (opens in a new browser tab)
Alliance Trading pH Down label Other source: “To add this product, broadcast into the deep end of the pool when not in use.” and “Do not add near metal fittings nor allow pH to drop below 7.2.” Source page (opens in a new browser tab)
CDC Official: “Never mix / Chlorine products with acid; this could create toxic gases” Source page (opens in a new browser tab)
UConn Health, Connecticut Poison Control Center, "Splish Splash Safety" Other source: “Keep acids away from other chemicals.” Source page (opens in a new browser tab)
Alliance Chemical 12.5% sodium hypochlorite safety data sheet Other source: “Never mix with acids, ammonia or other cleaning products: this releases toxic chlorine or chloramine gas.” Source page (opens in a new browser tab)
HTH Pool Care Shock, calcium hypochlorite 52% Other source: “Do not use this product in a floater or feeder.” Source page (opens in a new browser tab)
HTH 3" Chlorine Tabs Advanced Other source: “Do not use this product in floaters or feeders that have been used with other chlorinating products.” and “Do not use with any other tablets or sticks in the same skimmer, floater, or feeder.” Source page (opens in a new browser tab)
BioGuard cal-hypo label, EPA-accepted Other source: “Do not add this product to any dispensing device containing remnants of any other product.” Source page (opens in a new browser tab)
CDC Official, under “Never mix”: “Different pool chemicals (for example, different types of chlorine products) with each other or with any other substance” Source page (opens in a new browser tab)
CDC Official: “Only pre-dissolve pool chemicals when directed by product label” Source page (opens in a new browser tab)
Virginia Official: “Store chemicals in secure location away from children and pets.” Source page (opens in a new browser tab)
Virginia Official: “Never store liquid chemicals above dry chemicals.” Source page (opens in a new browser tab)
CDC Official: “Read chemical product label before each use” Source page (opens in a new browser tab)
Yakima County chart Official: “NOTE: This chart gives approximate amounts of each chemical listed. Always read the labels for exact” / “amounts needed for your chemical adjustments.” Source page (opens in a new browser tab)
Licking County Official: “Always follow instructions on the manufactures label for exact dosage amounts and handling.” Source page (opens in a new browser tab)
Multnomah County Official: “It is always better to add part of the required amount of chemical over several occasions” ... “than all at once (EXCEPTION: breakpoint chlorination).” Source page (opens in a new browser tab)
Indiana Official: “Add large amounts gradually in thirds over a 2-hour period.” Source page (opens in a new browser tab)
Our own rule for every result: we point you to your label and the official guidance instead.

Where calcium should be

It depends on the pool's surface. Multnomah County (Oregon) Environmental Health says The desirable range for a plaster pool is 200-400 ppm. and For a vinyl, painted, or fiberglass pool, 175 -300 ppm. The calculator raises calcium to the bottom of your surface's band unless you choose a higher target inside it.

How much calcium chloride

Amounts to raise calcium hardness by 10 ppm in 10,000 US gallons
Product	Amount	Source
Calcium chloride 77%	1.2 lb	Indiana Department of Health: Calcium Chloride (77%) 1.2 lbs 3.6 lbs 6.0 lbs.
Calcium chloride 100% (anhydrous)	0.9 lb	Indiana Department of Health: Calcium Chloride (100%) 0.9 lbs 2.8 lbs 4.6 lbs.

Other official charts give a little more for the calcium chloride 77% product, 1.25 lb; we start with the smaller amount. The first part is three quarters of the total, or the amount for 50 ppm if that is less, because calcium can usually only be removed by draining.

For example, say a plaster pool holds 20,000 US gallons and calcium hardness is 150 ppm. To reach 200 ppm the calculator estimates 12 lb in all, and says to add 9 lb (4,080 g) now, then wait, retest and work out the rest.

If calcium is too high

Calcium can usually only be lowered by replacing some of the water. The calculator gives no drain amount: talk to a pool professional before draining, because draining can damage some pools.

Above 1,000 ppm, the top of the national standard's range as quoted in a trade magazine (Pool water calcium hardness shall be maintained between a minimum of 150 and a maximum of 1,000 ppm as CaCO3.), the calculator sends you to a pool professional.

Add some, wait, retest

Test calcium hardness and note your pool's surface.
Put on the protective gear your label asks for, such as goggles and gloves. Make sure nobody is in the pool, and run the pump.
Add the first part as your label directs. Only pre-dissolve it in a bucket if the label tells you to. Add nothing else at the same time.
Wait at least 4 hours with the pump running, then retest and work out the rest.

Questions people ask

How do I raise calcium hardness in my pool?

Add calcium chloride in parts with the pump running. By the official chart, 1.2 lb of calcium chloride 77% raises calcium by 10 ppm in 10,000 US gallons. Wait at least 4 hours, retest, then add the rest.

How do I lower calcium hardness in my pool?

Usually only by replacing some of the water. Talk to a pool professional before draining: draining can damage some pools.

What should calcium hardness be?

Plaster pools 200–400 ppm; vinyl, fiberglass or painted pools 175–300 ppm (Multnomah County (Oregon) Environmental Health).

How long after adding calcium chloride can I swim?

We couldn't find a published figure for this. Follow your product's label, or ask a pool professional.

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The charts behind this page

Show all 10 figures and where each one comes from

Each figure this page and its calculator use. Open one for the source's own words, the other sources we checked it against, and the checks it has been through.

Acceptable calcium hardness range (pools): 150–1,000 ppm Other source
AQUA Magazine Other source says: Pool water calcium hardness shall be maintained between a minimum of 150 and a maximum of 1,000 ppm as CaCO3. Source page (opens in a new browser tab)
Also checked: Oregon Health Authority: Water Quality Standards, OAR 333-062-1000 (public pools) Official says: Calcium Hardness 200ppm 200-400ppm 2500ppm Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Ideal calcium hardness, plaster or concrete pool: 200–400 ppm Official
Multnomah County (Oregon) Environmental Health: Water Treatment - Swimming Pools, EHS-0058 Official says: The desirable range for a plaster pool is 200-400 ppm. Source page (opens in a new browser tab)
Also checked: Oregon Health Authority: Water Quality Standards, OAR 333-062-1000 (public pools) Official says: Calcium Hardness 200ppm 200-400ppm 2500ppm Source page (opens in a new browser tab)
Also checked: Pentair IntelliChlor IC15/20/40/60 Installation and User's Guide, P/N 520589 Rev R Other source says: 200 - 400 ppm Source page (opens in a new browser tab)
Also checked: Leslie's: Hardness Plus Other source says: The ideal range for calcium hardness in pool water is 200 to 400 ppm, Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure. Looked up again on 11/10/2026 by a checker who couldn't see our figure: it came back with the same figure.
Ideal calcium hardness, vinyl, painted or fiberglass pool: 175–300 ppm Official
Multnomah County (Oregon) Environmental Health: Water Treatment - Swimming Pools, EHS-0058 Official says: For a vinyl, painted, or fiberglass pool, 175 -300 ppm. Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Calcium chloride 77%: lb to raise calcium hardness 10 ppm in 10,000 US gal: 1.2 lb per 10 ppm per 10,000 US gal Official
Indiana Department of Health: Adjusting Chemical Levels in a Swimming Pool / Water Chemistry Adjustment Guide Official says: Calcium Chloride (77%) 1.2 lbs 3.6 lbs 6.0 lbs Source page (opens in a new browser tab)
Also checked: Salt Lake County Health Department (Utah): pool chemical dosages Official says: Calcium Chloride 77% 1 ¼ lb. 6 ¼ lb. 12 ½ lb. Source page (opens in a new browser tab)
Also checked: Yakima County (Washington): Chemical Dosing chart Official says: Calcium Chloride (77%) 1.25 pounds Source page (opens in a new browser tab)
Also checked: Leslie's: Hardness Plus Other source says: Adding 1.25 pounds of hardness plus to 10,000 gallons of water will raise the calcium hardness by 10 ppm. Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure. Looked up again on 11/10/2026 by a checker who couldn't see our figure: it came back with the same figure.
Calcium chloride 100% (anhydrous): lb to raise calcium hardness 10 ppm in 10,000 US gal: 0.9 lb per 10 ppm per 10,000 US gal Official
Indiana Department of Health: Adjusting Chemical Levels in a Swimming Pool / Water Chemistry Adjustment Guide Official says: Calcium Chloride (100%) 0.9 lbs 2.8 lbs 4.6 lbs Source page (opens in a new browser tab)
Also checked: Salt Lake County Health Department (Utah): pool chemical dosages Official says: Calcium Chloride 100% 1 lb. 5 lb. 10 lb. Source page (opens in a new browser tab)
Also checked: Yakima County (Washington): Chemical Dosing chart Official says: Calcium Chloride (100%) 1.0 pound Source page (opens in a new browser tab)
Also checked: Multnomah County (Oregon) Environmental Health: Water Treatment - Swimming Pools, EHS-0058 Official says: For every 10,000 gallons of water, adding 1 pound of calcium chloride will increase calcium hardness 11 ppm. Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Calcium chloride: wait before swimming: no published figure found Not confirmed
We couldn't find a published figure for this. Follow your product's label, or ask a pool professional.
Closest we found: Virginia Department of Health says NEVER add pool chemicals when the pool is in use, and only add them poolside as directed by the product label. Source page (opens in a new browser tab)
US gallon to liters: 3.785412 L per US gal Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: gallon (U.S.) (gal) | liter (L) | 3.785 412 | E+00 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
US fluid ounce to milliliters: 29.57353 mL per US fl oz Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: ounce (U.S. fluid) (fl oz) | milliliter (mL) | 2.957 353 | E+01 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Ounce (avoirdupois) to grams: 28.34952 g per oz Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: ounce (avoirdupois) (oz) | gram (g) | 2.834 952 | E+01 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.
Pound to kilograms: 0.4535924 kg per lb Official
NIST Special Publication 811, Appendix B.8 conversion factors Official says: pound (avoirdupois) (lb) | kilogram (kg) | 4.535 924 | E-01 Source page (opens in a new browser tab)
Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.