What Chemicals Are Used in Pool Service, and How to Handle Them

A CDC report in its Morbidity and Mortality Weekly Report (MMWR, 2019) found that the median estimated number of U.S. emergency department visits for pool chemical injuries was 4,535 per year during 2008 to 2017. In the 2015 to 2017 data, at least 56.3% of injuries occurred at a residence. If you are looking up what chemicals are used in pool service, you probably want two things: what each one does, and how not to become part of that statistic. Here is both, drawn from the CDC, EPA, UF/IFAS Extension, the Pool & Hot Tub Alliance (PHTA) and state health departments.

What chemicals are used in pool service, and what each one does

It is a short list. Nothing here is a dosing guide: products vary in strength, and the label governs.

• Chlorine sanitizer. The National Pesticide Information Center (NPIC, a cooperative of Oregon State University and the EPA) says "Antimicrobials such as chlorine and bromine kill bacteria that can cause recreational water illnesses." The CDC adds a caution: "Chlorine is added to the water to kill germs, but it does not work right away." Pool chlorine comes in several forms. NPIC lists dichlor, trichlor and calcium hypochlorite as active ingredients, and UF/IFAS Extension notes that pool chlorine products can contain "from 12 to 95 percent" chlorine.
• pH adjusters (acid and base). The CDC says keeping pH in the 7.0 to 7.8 range "best balances" killing germs, the lifespan of the pipes, and swimmers' comfort. To lower pH, pool operator manuals from the Illinois Department of Public Health (August 2000) and from a manual posted by an Idaho public health district name muriatic acid and sodium bisulfate. To raise it, they name soda ash (sodium carbonate). The PHTA says carbon dioxide leaving the water pushes pH up unless acid is added, and its fact sheet table shows that some chlorine products also move pH: trichlor decreases it, while sodium hypochlorite and calcium hypochlorite increase it.
• Cyanuric acid (stabilizer). The CDC calls it "a chlorine stabilizer." An Oregon public pool program fact sheet (April 2025) says it "helps protect free chlorine from breaking down in sunlight," and that it can be added separately or found in stabilized chlorine products such as trichlor and dichlor. The tradeoff: Oregon says it also "reduces chlorine's effectiveness to disinfect the water," which is why the CDC's chlorine minimum goes up when it is in the pool.
• Shock. This word has no single meaning. The EPA says its past enforcement decisions found that the term "shock" "is inherently a pesticide claim." It accepts labels such as "Oxidizes non-living swimmer waste" on non-pesticide oxidizer products, and recommends that they say "This product is neither a sanitizer nor algicide." The PHTA fact sheet refers to both chlorine shock and non-chlorine oxidizers, so check which one the bag is.
• Algaecide. A product made to kill algae. A swimming manual posted by an Idaho public health district defines it as "a specialty chemical which kills algae." NPIC says these products require EPA registration and carry an EPA registration number on the label.
• Alkalinity and calcium hardness. These are two more measurements in pool water balance. The PHTA fact sheet discusses both and notes that calcium hypochlorite leaves calcium behind, which raises hardness.

The CDC numbers worth writing down

The CDC's page "Home Pool and Hot Tub Water Treatment and Testing" gives the targets a homeowner can check against.

• pH: 7.0 to 7.8.
• Free chlorine: at least 1 ppm in pools, and at least 2 ppm in pools if you are using cyanuric acid or chlorine products with it.
• "As pH goes up, the ability of chlorine to kill germs decreases," and the CDC singles out pH above 8.0.
• Testing: the CDC recommends a DPD test kit, says test strips "are less accurate," and says to test chlorine and pH "at least twice per day."

Whatever you test with, the CDC says to follow the manufacturer's directions.

How to handle pool chemicals safely

The CDC's injury report found that people were most often hurt "when inhaling chemical fumes or dust (particularly while opening containers)," when chemicals were not secured away from children, or when chemicals were added just before someone got in the water. Its posters give a plain list.

• Lock chemicals up. The CDC poster says "Lock chemicals up to protect people and animals."
• Keep acid and chlorine apart: "Separate incompatible chemicals (for example, acid and chlorine)."
• Never mix them. The CDC says: "Never mix chlorine products with acid; this could create toxic gases." It also says not to mix "different pool chemicals (for example, different types of chlorine products) with each other or with any other substance." NPIC adds: "Never mix old products with new products of the same type."
• Keep every chemical "closed in original, labeled container."
• Store liquids low, per the CDC, "to prevent accidental contact."
• Wear "safety goggles and gloves," per the CDC. NPIC also lists long sleeves and pants.
• Read the whole label before every use, handle in a well-ventilated area, minimize dust, fumes and splashes, and open one container at a time and close it before opening another.
• Add chemicals to the water. The CDC says "NEVER add water to the pool chemical because a violent (potentially explosive) reaction can occur," and that you should pre-dissolve only when the label directs.
• Check the label's storage temperature. The CDC's toolkit for aquatics professionals says to store pool chemicals below 95°F (35°C) and in the conditions the manufacturer recommends, and to keep them dry.

If someone is exposed, NPIC says to follow the first aid instructions on the product label and to call Poison Control at 800-222-1222.

If you handle your own chemicals

A short routine you can start today without buying anything:

• Look at what you own. Find any product marked dichlor or trichlor, because that is a chlorine product with cyanuric acid, and the CDC's 2 ppm chlorine minimum applies.
• Check storage: acid and chlorine apart, liquids below dry products, nothing in an unlabeled container.
• Use a DPD kit for chlorine and pH. If you only have strips, treat the reading as a rougher guide, as the CDC does.
• If pH reads above 8.0, do not assume the chlorine is working at full strength. The CDC says its germ-killing ability decreases.
• Do not test pH after adding a chlorine shock. That is a testing note in the PHTA fact sheet.
• If a label and a blog post disagree, follow the label.

Where OneBlu fits

This post can tell you what the chemicals are and how to handle them. It cannot tell you your pool's numbers or replace a product label. If you would rather not store and handle these products yourself, OneBlu's Weekly Pool Care starts at $95 per month, and most standard residential pools fall between $95 and $189 per month. Your exact price is confirmed before service begins, and routine balancing chemicals are included unless the approved quote states otherwise. The visit checklist includes "Test and balance routine water chemistry," and the checklist ends with sending a digital service report with a photograph, readings and technician notes. The pricing page has the details, and the service areas page shows the cities OneBlu is accepting.