## What Is Cyanuric Acid?
Cyanuric acid (CYA) is a chemical compound with the formula C₃H₃N₃O₃. In pools, it does one job: it protects chlorine from UV degradation.
When CYA is in your water, it forms a weak bond with free chlorine molecules. The bond shields chlorine from sunlight. The bond is weak enough that chlorine can still break free to sanitize when needed.
**Names you’ll see:**
– Cyanuric acid (CYA)
– Pool stabilizer
– Pool conditioner
– Chlorine stabilizer
– Isocyanuric acid
**Where it comes from:**
You add CYA through standalone products or through your chlorine. Dichlor and trichlor tablets already contain CYA. Every time you use trichlor tablets, you add both chlorine and cyanuric acid to your pool.
This matters because trichlor tablets are the most popular chlorine form. If you use them regularly, your CYA level rises automatically. Many pools end up with CYA levels that are too high by mid-summer.
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## Ideal Cyanuric Acid Levels
The right CYA range depends on your pool type and how you sanitize:
| Pool Type | Ideal CYA Range | Maximum |
|———–|—————-|———|
| Chlorine pool (residential) | 30–50 ppm | 80 ppm |
| Saltwater pool | 60–80 ppm | 100 ppm |
| Commercial/public pool | 10–30 ppm | Varies by state |
Saltwater pools need more CYA because salt chlorine generators produce unstabilized chlorine. The higher CYA level compensates for continuous UV exposure between generation cycles.
**The FC/CYA ratio matters most:**
Your CYA level alone doesn’t tell the whole story. What matters is the ratio of free chlorine (FC) to CYA. The standard guideline is maintaining FC at 7.5% of your CYA level.
| CYA Level | Minimum Free Chlorine |
|———–|———————-|
| 30 ppm | 2 ppm |
| 40 ppm | 3 ppm |
| 50 ppm | 4 ppm |
| 60 ppm | 5 ppm |
| 80 ppm | 6 ppm |
| 100 ppm | 8 ppm |
High CYA creates problems. At 100 ppm CYA, you need 8 ppm of free chlorine to maintain sanitizing power. That’s expensive and hard to maintain.
> **???? Pro Tip:** Use the [Pool Chemical Calculator](https://poolchemicalcalculator.com) app to automatically calculate the right chlorine level based on your current CYA reading. It factors in the FC/CYA ratio so you never have to do the math yourself.
>
> ???? [Download for iPhone](https://itunes.apple.com/us/app/pool-chem-calculator/id1453351222) | [Download for Android](https://play.google.com/store/apps/details?id=com.poolchemicalcalculator.poolcalc)
—
## How to Add Cyanuric Acid to Your Pool
If your CYA is below the ideal range, follow these steps:
### Step 1: Test Your Current Level
Use a CYA-specific test. This means a turbidity test or reagent strip designed for CYA. Standard OTO/DPD chlorine tests do NOT measure cyanuric acid.
Most pool stores offer free water testing that includes CYA.
### Step 2: Calculate How Much You Need
For every 10 ppm increase in CYA per 10,000 gallons of water, you need approximately 13 ounces (0.8 lbs) of granular cyanuric acid.
**Example:** You have a 15,000-gallon pool. Current CYA is 20 ppm. Target is 40 ppm.
– Increase needed: 20 ppm
– Pool volume: 15,000 gallons (1.5 × 10,000)
– CYA needed: 13 oz × 2 × 1.5 = 39 oz (about 2.4 lbs)
### Step 3: Add It Properly
Cyanuric acid dissolves slowly. Here’s the best method:
1. Fill a 5-gallon bucket with warm pool water
2. Add the measured amount of granular CYA
3. Stir to partially dissolve (it won’t fully dissolve right away)
4. Pour the mixture slowly into the skimmer with the pump running
5. Alternative method: place CYA in a fine mesh sock and hang it in front of a return jet
**Important:** CYA takes 2–7 days to fully dissolve and register on a test. Don’t re-test and add more for at least 48 hours.
### Step 4: Retest After a Week
Wait a full week, then retest. If you’re still low, add more in small increments.
### Recommended Products
– [Clorox Pool&Spa Chlorine Stabilizer (4 lb)](https://www.amazon.com/dp/B08THFQQ16?tag=poolcalc04-20): Pure granular CYA, widely available
– [In The Swim Stabilizer & Conditioner (10 lb)](https://www.amazon.com/dp/B004BGAYVO?tag=poolcalc04-20): Bulk option for larger pools, great value
– [HTH Pool Care Stabilizer (4 lb)](https://www.amazon.com/dp/B000RQGLQE?tag=poolcalc04-20): Another reliable brand at most hardware stores
—
## How to Lower Cyanuric Acid
You can’t add a chemical to neutralize cyanuric acid. It doesn’t evaporate. It doesn’t break down. Standard filtration doesn’t remove it.
You have three options:
### Method 1: Drain and Refill (Most Common)
This is the most reliable method. Drain a portion of your pool water and replace it with fresh water.
**How to calculate:**
If your CYA is 120 ppm and you want to reach 40 ppm, you need to replace about 67% of your water (40 ÷ 120 = 0.33, meaning you keep 33%).
**Steps:**
1. Calculate how much water to drain
2. Use the main drain or a submersible pump
3. Never drain more than 1/3 at a time (to prevent the pool from popping out of the ground due to hydrostatic pressure)
4. Refill with fresh water
5. Run the pump for 24 hours
6. Retest
7. Repeat if needed
### Method 2: Bio-Active CYA Reducer
Products like [Natural Chemistry CYA Reducer](https://www.amazon.com/dp/B0DJJNH6ZQ?tag=poolcalc04-20) use a biological process to break down cyanuric acid. They work, with caveats:
– Takes 1–2 weeks to show results
– Effectiveness varies with water temperature
– More expensive than draining
– Best for pools where draining is impractical
### Method 3: Reverse Osmosis
Mobile pool water recycling services use RO membranes to filter out CYA and other dissolved solids without draining the pool.
This costs $400–$800 depending on pool size. It preserves your water, which can matter in drought areas.
—
## Why CYA Gets Too High (And How to Prevent It)
The number one cause of high CYA is trichlor tablets.
Every 3-inch trichlor tablet adds roughly 0.6 ppm of CYA per 10,000 gallons. This adds up fast:
– A typical pool uses 2–3 tablets per week
– Over a 6-month swim season, that’s 50+ tablets
– CYA accumulation: 30–50 ppm per season minimum
After 2–3 seasons without draining, you can easily hit 150+ ppm CYA. At that level, your chlorine is useless unless you maintain extremely high FC levels.
**Prevention strategies:**
– Use liquid chlorine (sodium hypochlorite) as your primary sanitizer. It adds zero CYA.
– Use trichlor tablets sparingly. Save them for convenience when you’re away.
– Add standalone CYA only when testing shows you need it. This gives you precise control.
– Partially drain your pool annually. Replace 1/4 to 1/3 of water each spring to reset CYA and other dissolved solids.
—
## Cyanuric Acid and Saltwater Pools
Saltwater pools have a unique relationship with CYA. The salt cell generates pure chlorine (sodium hypochlorite) which contains zero cyanuric acid.
This means:
1. You must add CYA separately. The salt cell won’t produce any.
2. CYA levels stay stable. Since you’re not adding stabilized chlorine, CYA won’t creep up.
3. Higher CYA is beneficial. The 60–80 ppm range helps chlorine last longer between cell generation cycles, reducing cell wear.
For saltwater pool owners, CYA management is simpler than chlorine pools. Add it once in spring, test monthly, and top off if it drops below 60 ppm.
—
## Common Cyanuric Acid Mistakes
**Mistake 1: Never testing CYA**
Many pool owners test pH and chlorine religiously. They never check CYA. You should test it monthly during swim season.
**Mistake 2: Adding CYA when using trichlor**
If your primary chlorine source is trichlor tablets, you probably don’t need to add standalone CYA. The tablets are already adding it.
**Mistake 3: Ignoring high CYA because chlorine reads normal**
A test kit showing 3 ppm FC at 100+ ppm CYA means your chlorine has almost no sanitizing power. The FC/CYA ratio is what matters.
**Mistake 4: Trying to burn off CYA with shock**
Shocking your pool does NOT lower CYA. This is a persistent myth. Shock (calcium hypochlorite or sodium hypochlorite) only addresses chlorine demand. It has no effect on cyanuric acid levels.
**Mistake 5: Adding too much CYA at once**
CYA takes days to dissolve and register. Adding a second dose before the first fully dissolves leads to overshooting your target.
—
## Frequently Asked Questions
**Q: How often should I test cyanuric acid?**
Test CYA at least once per month during swimming season. If you use trichlor tablets, test every 2 weeks because levels can rise quickly. At pool opening and closing, always test CYA as part of your complete water analysis.
**Q: Can cyanuric acid hurt you?**
At normal pool levels (30–80 ppm), cyanuric acid is safe for swimmers. It’s also non-toxic to pool equipment. The concern with high CYA is that it reduces chlorine effectiveness. This means your pool isn’t properly sanitized, which creates the real health risk.
**Q: Does cyanuric acid lower pH?**
Cyanuric acid is mildly acidic (pH around 2.8 in pure form). Adding it can slightly lower pH and total alkalinity. However, the effect is minimal at typical doses. Always retest pH after adding CYA and adjust if needed.
**Q: How long does cyanuric acid last in pool water?**
CYA is extremely stable. It doesn’t evaporate. It doesn’t break down in sunlight. Standard filtration doesn’t remove it. The only ways it leaves your pool are through water loss (splashing, backwashing, leaks, draining) and very slow biological degradation.
**Q: Can I use cyanuric acid in an indoor pool?**
No. Indoor pools don’t receive UV exposure, so there’s no benefit to adding CYA. Adding it to an indoor pool would only reduce chlorine effectiveness without providing any protective benefit.
—
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## Keep Your Pool Chemistry Balanced
Cyanuric acid protects your chlorine from the sun. Without it, you waste money replacing chlorine that UV rays destroy in hours. With too much, your chlorine stops working even when test strips say it’s there.
Most residential pools should maintain 30–50 ppm CYA. Keep your free chlorine at roughly 7.5% of your CYA level. Test monthly. Watch for trichlor tablet accumulation. Partially drain when levels get too high.
The **Pool Chemical Calculator** app handles the FC/CYA ratio math automatically and gives you personalized dosing recommendations.
???? [Download for iPhone](https://itunes.apple.com/us/app/pool-chem-calculator/id1453351222) | [Download for Android](https://play.google.com/store/apps/details?id=com.poolchemicalcalculator.poolcalc) | ???? [Web Version](https://poolchemicalcalculator.com)
**Related Articles:**
– [Pool Chemicals: The Complete Guide](https://poolchemicalcalculator.com/news/pool-chemicals)
– [Pool Water Chemistry: Everything You Need to Know](https://poolchemicalcalculator.com/news/pool-water-chemistry)
– [Pool Shock Treatment: When, Why, and How](https://poolchemicalcalculator.com/news/pool-shock-treatment)
– [Pool Chlorine Levels: The Complete Guide](https://poolchemicalcalculator.com/news/pool-chlorine-levels)