Chlorine types compared: liquid, bleach, cal-hypo, dichlor, trichlor and salt
All pool chlorine ends up as the same thing in the water: free chlorine. What differs is how strong the product is, how you dose it, and what it leaves behind — stabilizer, calcium or salt. Those leftovers decide which one suits your pool, so they are worked out here from the chemistry rather than guessed.
Chlorine types side by side
| Type | Strength on the label | +1 ppm in 10,000 gal | Also adds, per 1 ppm of chlorine | Effect on pH | Usual use |
|---|---|---|---|---|---|
| Liquid chlorine (sodium hypochlorite) | 10% or 12.5% | 10.2 fl oz (1.3 cups) of 12.5% | About 1.65 ppm salt, once used | Alkaline in the jug; most of the rise reverses as the chlorine is used. A small upward drift is common. | Daily dosing and shocking |
| Household bleach (plain, unscented) | 5–8.25% sodium hypochlorite | 21.3 fl oz (2.7 cups) of 6% | About 1.65 ppm salt, once used | Same as liquid chlorine | Small pools and hot tubs; same chemical, weaker |
| Cal-hypo (calcium hypochlorite) | 65–73% available chlorine | 2.1 oz of 65% | About 0.71 ppm calcium hardness | Raises pH when added; much of it reverses as the chlorine is used | Granular shock, pre-dissolved |
| Dichlor (sodium dichloroisocyanurate) | 55–56% (dihydrate); about 62% anhydrous | 2.4 oz of 56% | About 0.91 ppm stabilizer (CYA) | Close to neutral when added; mildly acidic over time | Hot tubs; quick shock in pools |
| Trichlor (trichloroisocyanuric acid) | 90% | 1.5 oz (one 7 oz tablet ≈ 4.7 ppm) | About 0.61 ppm stabilizer (CYA) | Strongly acidic: pulls pH and alkalinity down | Tablets in a floater or feeder |
| Salt chlorine generator | Makes chlorine from salt kept at about 3,200–3,600 ppm (Hayward and Pentair targets) | Set by cell output and run time | Nothing net: the salt is turned back into salt as chlorine is used | Neutral on paper; pH often drifts up in practice, so expect to add acid | Continuous dosing in pools |
| Non-chlorine shock (monopersulfate) | Not chlorine | Adds no free chlorine | Sulfate | Acidic; can lower pH and alkalinity a little | Oxidizing between chlorine doses; not a sanitizer |
Bigger rises scale in a straight line — 3 ppm takes three times the 1 ppm figure. The full set for 1, 3, 5 and 10 ppm is in the pool chemical dose chart, and the worked pages do it for a whole pool: how much chlorine for a 10,000 gallon pool, how much chlorine for a 15,000 gallon pool and how much chlorine for a 20,000 gallon pool.
What “available chlorine” means
The percentage on a bag of granules or tablets is available chlorine: how much the product can oxidize, expressed as if it were chlorine gas, as a share of its weight. That is why trichlor is “90%” even though it is not 90% chlorine atoms, and why cal-hypo is sold at 65% one shelf over from 73%. Liquid strengths are usually read as grams of chlorine per 100 ml (the bleach trade’s “percent”), so 12.5% liquid holds about 125 g of chlorine per litre. Some jugs state 12.5% sodium hypochlorite by weight instead, which one supplier’s data sheet puts at about 142 g per litre — a little stronger.
grams of chlorine needed = ppm rise × litres of water ÷ 1,000 product needed = grams ÷ available-chlorine fraction
What each one leaves behind
This is the part that matters over a season. Every ppm of chlorine you add brings its carrier along, and chlorine is used up but the carrier is not.
Salt from hypochlorite: 2 × 58.44 ÷ 70.91 = 1.65 ppm per ppm FC Calcium from cal-hypo: 100.09 ÷ (2 × 70.91) = 0.71 ppm CH per ppm FC CYA from dichlor: 129.07 ÷ (2 × 70.91) = 0.91 ppm per ppm FC CYA from trichlor: 129.07 ÷ (3 × 70.91) = 0.61 ppm per ppm FC
To see what that adds up to, imagine a pool that uses 2 ppm of chlorine a day for 90 days — 180 ppm in all — and gets every bit of it from one product:
| If all the chlorine came from… | It would also add |
|---|---|
| Liquid chlorine or bleach | About 297 ppm of salt |
| Cal-hypo | About 127 ppm of calcium hardness |
| Dichlor | About 164 ppm of stabilizer |
| Trichlor | About 109 ppm of stabilizer |
| Salt generator | No net change; salt only leaves with splash-out, backwash and rain overflow |
Salt is harmless at those levels (a salt pool runs ten times more on purpose). Calcium matters on plaster but is rarely a problem from cal-hypo alone. Stabilizer is the one that bites: the Model Aquatic Health Code caps it at 90 ppm in public pools, and the more CYA in the water, the more chlorine you need every day. A pool on tablets all summer can end up needing a partial drain — see how much water to drain to lower CYA.
How to choose
- Liquid chlorine is the simplest all-rounder: no stabilizer or calcium, easy to measure, and it doubles as shock. It is heavy to carry and loses strength in storage. Start with how much liquid chlorine to raise 1 ppm in 10,000 gallons.
- Bleach is the same chemical at about half the strength. Plain, unscented only — see how much bleach for a 10,000 gallon pool.
- Trichlor tablets are the convenient choice: drop them in a floater and they dose for a week. The price is steady stabilizer and acid build-up. How many chlorine tablets for a 10,000 gallon pool and for a 20,000 gallon pool show the CYA climbing week by week.
- Cal-hypo is a granular shock that adds no stabilizer. Pre-dissolve it in a bucket of pool water (chemical into water) so the granules don’t sit on a liner. How much shock for a 10,000 gallon pool and how much shock for a 20,000 gallon pool compare it with liquid.
- Dichlor dissolves fast and is close to neutral, which is why spa owners use it — but the CDC recommends no stabilizer in hot tubs, so dichlor users have to drain and refill often enough to keep CYA from building. In a hot tub, how much bleach to put in a hot tub is the stabilizer-free alternative.
- Salt generators make chlorine from dissolved salt, so you buy salt once and top it up. You still test, and you still need stabilizer outdoors — see what CYA and chlorine a salt water pool needs and how much salt for a 15,000 gallon pool.
For algae, any chlorine works if you can reach and hold the level your stabilizer calls for. In practice that means liquid chlorine: reaching 16–20 ppm with dichlor or trichlor would add a lot of stabilizer at once. How much liquid chlorine to SLAM a pool works through it.
Storage and the never-mix rule
The CDC estimates that pool chemical injuries lead to 3,000–5,000 emergency department visits a year (MMWR, 2019). The rules that prevent most of them are simple:
- Never mix chemicals, especially chlorine with acid (that releases chlorine gas), and never mix two kinds of chlorine. Cal-hypo and trichlor in particular must not meet; the CDC’s storage poster says not to mix different chlorine products.
- Store acid and chlorine apart, in their original labelled containers, in a cool, dry, ventilated place out of the sun, with liquids on low shelves. The CDC toolkit says to keep them below 95°F (35°C).
- One scoop, one chemical. Don’t reuse containers or measuring cups across products.
- Add chemical to water, never water to chemical, one product at a time, with the pump running, and keep children away.
- The label is the law. Pool chlorine is an EPA-registered pesticide; follow the label’s dose, swimming limits and storage.
Frequently asked questions
Which types of pool chlorine add stabilizer?
Only the stabilized ones: trichlor (about 0.6 ppm CYA per ppm of chlorine) and dichlor (about 0.9). Liquid chlorine, bleach, cal-hypo and salt generators add none.
Is pool liquid chlorine stronger than bleach?
Yes, usually about twice as strong: pool chlorine is 10–12.5%, household bleach 5–8.25%. It is the same chemical, sodium hypochlorite, so you simply use more bleach for the same rise.
Can I switch from chlorine tablets to liquid chlorine mid-season?
Yes. Stop the tablets, rinse the feeder, and dose liquid by your free chlorine test. Stabilizer already in the water stays, so keep chlorine at the level your CYA calls for.
Sources
- OxyChem — Soda Bleach Solutions Handbook (re-hosted copy) (opens in a new tab) — Trade percent = grams per litre of available chlorine ÷ 10; weight % NaOCl ≈ 1.05 × weight % available chlorine; strength and specific gravity table.
- HASA — Hasachlor sodium hypochlorite SDS (2026) (opens in a new tab) — Pool liquid chlorine: sodium hypochlorite 12.5% by weight, about 1.2 g/ml.
- Hill Brothers — Sodium hypochlorite 12.5% specifications (opens in a new tab) — 12.5% by weight = 142 g/L available chlorine (14.2 trade percent), 11.9% available chlorine by weight.
- Pool Essentials chlorinating liquid (retail listing) (opens in a new tab) — A 10% sodium hypochlorite pool chlorine.
- Clorox Regular Bleach SDS (2020) (opens in a new tab) — Household bleach: sodium hypochlorite 5–10% by weight.
- US EPA label 57787-18 — calcium hypochlorite 65% (opens in a new tab) — 65% available chlorine; 2 oz per 10,000 gallons raises chlorine about 1 ppm; superchlorinate with 10 oz per 10,000 gallons.
- US EPA label 1258-161 — HTH calcium hypochlorite 73% (opens in a new tab) — Calcium hypochlorite 73% (70% minimum available chlorine); a 1 lb bag shock-treats 15,000 gallons.
- US EPA reg. 42177-80 — sodium dichlor label (ProPools copy) (opens in a new tab) — Dihydrate, 56% available chlorine; 2–3 oz per 10,000 gallons daily; 1 lb per 10,000 gallons to superchlorinate.
- ICC Building Safety Journal (PHTA Recreational Water Quality Committee) — Trichlor: the dependable pool performer (opens in a new tab) — Trichlor is 90% available chlorine and adds 0.6 ppm cyanuric acid for each ppm of chlorine.
- US EPA label 36284-5 — 3 in trichlor tablet (7 oz) (opens in a new tab) — 90% available chlorine; one tablet gives 4.7 ppm in 10,000 gallons; 1 tablet per 8,000 gallons every 7–14 days to maintain.
- Hayward — AquaRite salt chlorination owner’s manual (092538 Rev D) (opens in a new tab) — Ideal salt 2,700–3,400 ppm, 3,200 ppm optimal.
- Pentair — IntelliChlor Plus / LT owner’s manual (opens in a new tab) — Ideal salt 3,600 ppm, range 2,600–4,500 ppm.
- CDC — Model Aquatic Health Code, 5th edition (2024), code (opens in a new tab) — Free chlorine minimum 1.0 ppm (2.0 with CYA, 3.0 in spas); pH 7.0–7.8; CYA at or below 90 ppm; CYA:FC above 45:1 is an imminent hazard; TA 60–180 ppm; turnover tables.
- CDC Healthy Swimming — Home pool and hot tub water treatment and testing (opens in a new tab) — pH 7.0–7.8; free chlorine at least 1 ppm in pools (2 ppm with cyanuric acid) and 3 ppm in hot tubs; no CYA in hot tubs; test twice a day.
- CDC — Pool chemical injuries press release (2014) (opens in a new tab) — Never mix pool chemicals, especially chlorine products with acid; add chemical to water, never water to chemical.
- CDC — Pool chemical safety: storage poster (opens in a new tab) — Separate acid and chlorine; don’t mix different types of chlorine; keep chemicals cool, dry and in original containers.
- CDC Healthy Swimming — Pool chemical safety toolkit (opens in a new tab) — Store pool chemicals below 95°F (35°C).
- CDC MMWR — Pool chemical–associated health events (2019) (opens in a new tab) — An estimated 3,000–5,000 emergency department visits a year from pool chemical injuries.
- US EPA — Introduction to pesticide labels (opens in a new tab) — Pool sanitizers are registered pesticides; the label is the law.
- US EPA — Use of the term “shock” on pool and spa products (opens in a new tab) — “Shock” is a pesticide claim; products must be registered and used as labelled.