Pool chemistry guide

Pool Shock Dosage Chart

How much shock a pool needs depends on two things the charts usually blur together: how much water you are treating, and which product you are holding. This chart keeps cal-hypo, dichlor and liquid chlorine apart, because they are not interchangeable.

By Ellyana, creator of CalcClearly · Published 2026-09-06 · Last reviewed 2026-09-06

Short answer

For routine maintenance: 1 lb of 65–73% cal-hypo per 10,000 gallons, or about 1.2 lb of dichlor, or 1 gallon of 10–12.5% liquid chlorine. Double it for cloudy water and triple it for a green pool. So a 15,000-gallon pool takes 1.5 lb of cal-hypo for maintenance, 3 lb if cloudy, and 4.5 lb if green. Add it at dusk with the pump running, and check your own product label first — available chlorine varies by brand.

The Chart

Doses by pool volume and product. Each block is one product type — read down your volume, across to your water condition. Do not add two of these products to the same treatment.

Cal-hypo (65–73%)

The default for most home pools.

Pool volume	Maintenance	Cloudy	Green / algae
5,000 gal	0.5 lb	1 lb	1.5 lb
8,000 gal	0.8 lb	1.6 lb	2.4 lb
10,000 gal	1 lb	2 lb	3 lb
12,000 gal	1.2 lb	2.4 lb	3.6 lb
15,000 gal	1.5 lb	3 lb	4.5 lb
20,000 gal	2 lb	4 lb	6 lb
25,000 gal	2.5 lb	5 lb	7.5 lb
30,000 gal	3 lb	6 lb	9 lb

Dichlor (56–62%)

Adds cyanuric acid with every dose.

Pool volume	Maintenance	Cloudy	Green / algae
5,000 gal	0.6 lb	1.2 lb	1.8 lb
8,000 gal	1.0 lb	1.9 lb	2.9 lb
10,000 gal	1.2 lb	2.4 lb	3.6 lb
12,000 gal	1.4 lb	2.9 lb	4.3 lb
15,000 gal	1.8 lb	3.6 lb	5.4 lb
20,000 gal	2.4 lb	4.8 lb	7.2 lb
25,000 gal	3 lb	6 lb	9 lb
30,000 gal	3.6 lb	7.2 lb	10.8 lb

Liquid chlorine (10–12.5%)

Already dissolved; adds no calcium.

Pool volume	Maintenance	Cloudy	Green / algae
5,000 gal	0.5 gal	1 gal	1.5 gal
8,000 gal	0.8 gal	1.6 gal	2.4 gal
10,000 gal	1 gal	2 gal	3 gal
12,000 gal	1.2 gal	2.4 gal	3.6 gal
15,000 gal	1.5 gal	3 gal	4.5 gal
20,000 gal	2 gal	4 gal	6 gal
25,000 gal	2.5 gal	5 gal	7.5 gal
30,000 gal	3 gal	6 gal	9 gal

Maintenance is clear water on a weekly routine. Cloudy is dull or hazy water, usually chloramines after heavy use. Green means visible algae — brush the walls and floor first so the chlorine can reach what is clinging to them.

Never Treat the Three as Interchangeable

Never mix them. The CDC's guidance is to store each pool chemical separately and keep incompatible products apart. Cal-hypo and dichlor react with one another, and the combination can ignite. Chlorine mixed with acid produces chlorine gas. Mixing incompatible products is among the leading causes of the roughly 13,500 US emergency department visits a year that pool chemicals produce.

That applies to the water as well as the container: add one product, let it circulate fully, and leave any other treatment for a separate occasion.

And they are not equivalent even used separately, because each leaves something behind:

Cal-hypo adds calcium. Fine occasionally; over seasons it raises calcium hardness and eventually shows up as scale.
Dichlor adds cyanuric acid every single dose. CYA protects chlorine from sunlight, which is useful up to a point, but it does not leave the water except by dilution. Used as your regular shock it climbs until chlorine stops working properly, and the only remedy is replacing water.
Liquid chlorine adds neither, which is why it suits pools already high in calcium or CYA. The trade-offs are that it loses strength within weeks in storage and you carry far more volume for the same dose.

So the right product depends on what your water already has too much of, not on which chart row looks cheapest.

Before You Add Anything

Read your own label. Available chlorine varies between brands within the same product type, and the label's directions override this chart.
Wear eye protection and gloves, and open the container away from your face. Dust and fumes released on opening injure people every season.
If pre-dissolving, add the chemical to the water — never water to the chemical. The CDC warns the reverse can cause a violent, potentially explosive reaction.
Add at dusk or after dark, with the pump running. Unstabilised chlorine is destroyed by sunlight within hours, so a midday dose can be largely gone before it has finished working. This is a common reason a pool stays green after what looked like a full treatment.
Brush first if the water is green, so the chlorine reaches algae on the surfaces rather than only in open water.
Nobody swims until you have tested. EPA-registered pool chlorine labels prohibit re-entry above 4 ppm of chlorine. See the guide on when it is safe to swim.

If the Dose Does Not Seem to Work

Three things account for most cases where a correct dose has no visible effect.

Cyanuric acid is too high. CYA shields chlorine from sunlight, but above a certain level it also holds chlorine in a form that sanitises poorly. A pool with very high CYA needs far more chlorine to achieve the same effect, and the practical fix is partial draining and refilling rather than more shock. If you have been using dichlor or trichlor tablets all season, this is the first thing to check.

pH is too high. Chlorine sanitises much less effectively above roughly pH 7.8. A pool that will not hold chlorine often has a pH problem rather than a chlorine problem — see the muriatic acid guide.

The demand was larger than the dose. Heavy algae consumes chlorine quickly. If the water improved but did not clear, the treatment worked and was simply used up; a second dose the next day is normal rather than a sign something is wrong.

Common questions

For routine maintenance, 1 lb of 65–73% cal-hypo per 10,000 gallons, which raises free chlorine by roughly 5–10 ppm. The equivalent is about 1.2 lb of dichlor or 1 gallon of 10–12.5% liquid chlorine. Double all of those for cloudy water and triple them for a green pool. Your product label is the authority — available chlorine varies between brands even within a product type.

No. Never mix pool chemicals of any kind. Cal-hypo and dichlor react with each other and the combination can ignite. The CDC records mixing incompatible products as a leading cause of pool chemical injury. Pick one product for a given treatment, add it, let the pump circulate it, and if you are switching products between treatments, wait until the first has fully dispersed.

Roughly, at the maintenance dose — both deliver a broadly similar amount of available chlorine per 10,000 gallons. But they are not interchangeable in any deeper sense. Cal-hypo adds calcium, which accumulates as hardness. Liquid adds none but degrades within weeks in storage. Dichlor adds cyanuric acid every time, which is useful once and a problem all season. Choose on those side effects, not on the headline dose.

Because it carries less available chlorine by weight — around 56–62% against cal-hypo's 65–73%. That is why the dichlor column here is higher. The more consequential difference is that dichlor is stabilised: every dose adds cyanuric acid, and CYA does not leave the water except by dilution. Used all season it climbs until your chlorine stops working properly at normal levels.

Yes. A salt chlorine generator produces chlorine continuously at a low rate, which handles routine sanitising but does not deliver the large one-off dose needed to break down chloramines or clear algae. Most generators have a "superchlorinate" or "boost" setting for this, and many owners still add shock directly after heavy use or a fouling incident.

Check your label; some products call for pre-dissolving and some for broadcasting directly. If you do pre-dissolve, the CDC is explicit that you add the chemical to water and never water to the chemical, because the reverse can cause a violent and potentially explosive reaction. Fill the bucket first, then add the granules slowly.

Test. Free chlorine should be well above your normal target immediately after shocking, then fall back over the following day or so. If it barely moved, the dose was consumed by whatever you were treating and a second one is likely needed. If it did not move at all and the water is green, check your cyanuric acid — very high CYA locks chlorine up and no amount of shock at normal doses will fix it.

Sources

CDC — Pool Chemical Safety — Store each pool chemical separately and keep incompatible products apart; add pool chemical to water, never water to pool chemical.
CDC — Home Pool and Hot Tub Water Treatment and Testing — Recommends pH 7.0–7.8 and free chlorine of at least 1 ppm in pools, or at least 2 ppm where cyanuric acid is in use, tested at least twice a day.
CDC — Pool Chemical Injuries in Public and Residential Settings, MMWR 68(19) — Mixing incompatible products, spills, missing protective equipment, and fumes released when opening a container are among the leading contributing factors to injury.
Manufacturer labelling for calcium hypochlorite shock — The 1 lb per 10,000 gallon baseline used here reflects label directions for 65% and 73% cal-hypo products, which state that this provides roughly 5–10 ppm of available chlorine. Available chlorine differs between brands; your own label takes precedence.

About this guide. Written and maintained by Ellyana, who created CalcClearly. No pool-industry or chemistry qualification is claimed here. What can be checked is the sourcing: every figure on this page comes from the CDC guidance and the EPA-registered product labelling listed under Sources, each dosing figure is generated by the same model the calculator runs on, and a test fails the site build if the two ever disagree. It is general guidance, not a substitute for the directions on your own product.

Last reviewed 2026-09-06. General guidance for domestic pools only. The directions on the product you actually bought take precedence over anything written here, and public or commercial pools are subject to separate local health regulations.