Pool-chemical safety: Stabilizer is a pool chemical too. HTH’s safety directions for its stabilizer say “Do not mix this product with any other chemicals,” and CDC’s chemical-use poster says never to mix different pool chemicals and never to add water to a pool chemical.
Stabilizer, or cyanuric acid (CYA), protects chlorine from sunlight in outdoor pools, but it also slows how quickly chlorine kills germs. Keep it inside the range your authority or equipment maker gives, raise free chlorine as CYA rises, and expect to lower it only by draining part of the water and refilling. Trichlor tablets and dichlor shock add CYA every time you use them, so a tablet-fed pool climbs steadily.
What the authorities and makers say
There is no single number every source agrees on. Here is what each one publishes:
| Source | What it says about CYA |
|---|---|
| CDC home pool guidance | With CYA or stabilized chlorine, keep free chlorine at least 2 ppm in pools; don’t use CYA in hot tubs |
| CDC 2024 MAHC (public pools) | CYA at or below 90 ppm; 300 ppm or higher closes the pool; none in new spas or therapy pools |
| PHTA, as listed in Pentair’s IntelliChlor manual | 0–50 ppm ideal; Pentair adds “DO NOT USE CYANURIC ACID IN INDOOR POOLS” |
| Hayward AquaRite manual | 30–50 ppm outdoor (US), 0 ppm indoor |
| CircuPool CORE manual | 30–50 ppm; “should not typically be kept above 50 ppm” |
| Clorox Chlorine Stabilizer page | Test weekly so stabilizer “remains at least 30 ppm” |
The MAHC is written for public pools and is not binding on a backyard pool, but its 90 ppm cap is a published public-health ceiling. The salt-system ranges apply to pools using those systems. If you run a salt system, follow its manual first.
Why more stabilizer is not better
The MAHC annex explains that “CYA reversibly binds CHLORINE and reduces the aqueous concentration of HOCl,” which it identifies as the primary disinfecting form of chlorine, and that “CYA is not a DISINFECTANT.” CDC’s home pool guidance notes that “disinfection times are longer in the presence of cyanuric acid.”
CDC’s minimum free chlorine doubles from 1 ppm to 2 ppm when you use stabilizer, which the MAHC annex describes as a “SAFETY factor of 2.” The annex goes further: free chlorine “should be increased proportionally as the CYA concentration rises.” So the same free chlorine reading does less disinfecting as CYA climbs.
How tablets build it up
The MAHC annex says CYA “associates with CHLORINE to form chlorinated isocyanurates: trichlor (trichloroisocyanuric acid) and dichlor (sodium dichloroisocyanuric acid).” It adds that trichlor is commonly sold as tablets or sticks, and dichlor as a granular material.
The labels say the same thing in plainer words. The label for Clorox Active99 tablets states that the product “contains both chlorine and a stabilizer which reduces chlorine loss from sunlight.” HTH says its 3-inch Advanced tablets “contain approximately 57% cyanuric acid by weight” and advises switching to its cal hypo tablets when CYA nears 50 ppm.
CYA keeps rising for as long as the tablets keep dissolving. If you run a salt system, Pentair’s manual warns against adding trichlor or dichlor at all.
How to raise stabilizer
Raise it only after a test shows it is low, and only with a product labeled for it.
- Test first. Use a kit that reads CYA. The Taylor K-2006 (a labeled Amazon search) includes a cyanuric acid test that Taylor lists in steps from 30 to 100 ppm. The test kit list compares others.
- Use the dose chart for the exact product. As an example, here is HTH’s chart for HTH Pool Care Chlorine Stabilizer (SKU 67061). It applies to that product only:
| Pool size (gallons) | Raise 10 ppm | Raise 20 ppm | Raise 30 ppm | Raise 40 ppm |
|---|---|---|---|---|
| 5,000 | 8 oz | 1 lb | 1.5 lb | 2 lb |
| 10,000 | 1 lb | 2 lb | 3 lb | 4 lb |
| 15,000 | 1.5 lb | 3 lb | 4.5 lb | 6 lb |
| 20,000 | 2 lb | 4 lb | 6 lb | 8 lb |
- Add it the way the label says. HTH’s directions: turn on the pump, add the dose “slowly to the skimmer,” keep the pump running and don’t backwash for 48 hours. HTH notes that CYA dissolves slowly, so retest only after the wait printed on your container.
- Recheck pH and alkalinity. HTH notes that cyanuric acid “may slightly lower pH and alkalinity when added in large doses.” The pH and alkalinity guide covers correcting them.
Clorox Pool&Spa Chlorine Stabilizer comes in a 4 lb size, but Clorox’s product page does not publish a dose chart, so use the directions on the container.
How to lower stabilizer
Dilute it. HTH says “the only reliable way to lower CYA is to partially drain and refill the pool.” The MAHC annex, describing remediation in public pools, says the pool “will need to be partially drained and refilled to reduce the CYA concentration,” and that “alternate methods of reducing the CYA concentration are acceptable, as long as test data shows” the lower level. In practice that means:
- Stop adding it. Switch to a chlorine source without CYA while you bring it down: cal hypo or liquid chlorine (see the pool shock comparison ), or a salt chlorine generator .
- Drain part of the water and refill with fresh water, following your pool builder’s or liner maker’s limits on how far to drain.
- Retest CYA, then rebalance pH, alkalinity, calcium and, on a salt pool, salt.
If a reading is off the top of your test’s scale, the true level may be higher than shown. The MAHC annex notes that 100 ppm “is the maximum concentration measured in the turbimetric test without diluting the sample.”
Indoor pools and hot tubs
CDC recommends not using cyanuric acid or chlorine products containing it in hot tubs. The MAHC annex adds that “CDC does not recommend CYA use for indoor AQUATIC VENUES.” Hayward lists 0 ppm for indoor pools, and Pentair says not to use it indoors.
Sources
- CDC: Home Pool and Hot Tub Water Treatment and Testing
- CDC: Use Pool Chemicals Safely poster
- CDC: 2024 Model Aquatic Health Code and annex
- Pentair IntelliChlor Plus and LT installation and user’s guide
- Hayward AquaRite owner’s manual
- CircuPool CORE Series manual
- HTH Pool Care Chlorine Stabilizer and HTH 3" Chlorine Tabs Advanced
- Clorox Pool&Spa Chlorine Stabilizer
- EPA-accepted label, Clorox registration 67262-17
- Taylor K-2006 Complete test kit
Facts were checked against these sources on October 9, 2026. This guide summarizes published guidance and labels; it is not based on hands-on testing.
FAQ
What should my pool’s stabilizer (CYA) level be?
It depends on whose guidance you follow. The salt-system manuals from Hayward and CircuPool give 30 to 50 ppm for outdoor pools, Pentair’s manual lists PHTA’s 0 to 50 ppm, and the MAHC caps public pools at 90 ppm. Indoor pools and hot tubs should not use it, according to CDC, Hayward and Pentair.
Do chlorine tablets raise stabilizer?
Yes. Trichlor tablets and dichlor granules are chlorine combined with cyanuric acid, so CYA rises with every dose. Clorox’s Active99 label says the tablets contain both chlorine and a stabilizer.
How do you lower stabilizer in a pool?
The MAHC annex names partial draining and refilling, and accepts other methods only when test data confirm the lower level. HTH says the only reliable way is to partially drain and refill.
Does high stabilizer mean I need more chlorine?
Yes. CDC recommends at least 2 ppm free chlorine instead of 1 ppm when you use stabilizer, and the MAHC annex says free chlorine should rise in proportion as CYA rises.