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Pool Stabilizer Calculator
Calculate how much cyanuric acid (CYA) to add to protect chlorine from UV rays.
Prevent chlorine loss from sunlight and reduce chemical costs.
No sign-ups. Instant results.
⚠️ Stabilizer above 80 ppm causes "chlorine lock" — water won't sanitize properly even with high chlorine. The only fix is to drain and refill.
Example calculation
Let's say you have a 20,000 gallon pool with a current stabilizer level of 20 ppm and you want to raise it to 40 ppm:
| Input | Value |
|---|---|
| Pool volume | 20,000 gallons |
| Current stabilizer (CYA) | 20 ppm |
| Target stabilizer | 40 ppm |
| Increase needed | 20 ppm |
| Cyanuric acid needed | 2.6 pounds (42 ounces) |
Formula: (pool gallons / 10,000) × (ppm increase / 10) × 13 oz = ounces needed
(20,000 / 10,000) × (20 / 10) × 13 = 52 oz ≈ 2.6 lbs
Stabilizer level guide
| CYA Level | Effect on Pool | Action Needed |
|---|---|---|
| 0-20 ppm | Chlorine breaks down rapidly in sunlight (90% loss in 2 hours) | Add stabilizer immediately |
| 30-50 ppm | ✅ Ideal range - chlorine protected, still effective | No action needed |
| 60-80 ppm | Chlorine effectiveness reduced by 20-30% | Avoid adding more stabilizer |
| Above 80 ppm | ⚠️ Chlorine lock - sanitizer doesn't work properly | Must drain and refill |
How to add cyanuric acid to your pool
Method 1: Dissolve in bucket (recommended)
Best for: Granular cyanuric acid
How: Fill a 5-gallon bucket with warm pool water. Slowly add cyanuric acid while stirring.
Continue stirring until mostly dissolved (takes 10-15 minutes). Pour dissolved mixture around pool perimeter
with pump running. Undissolved granules will settle and slowly dissolve over 24-48 hours.
Method 2: Sock in skimmer
Best for: Small amounts (1-2 lbs)
How: Place granular stabilizer in an old sock or nylon stocking. Tie off the end. Place in
the skimmer basket with pump running. Check every few hours and knead sock to help dissolve. Remove sock when
empty (24-48 hours). This method takes longer but avoids cloudy water.
Method 3: Liquid stabilizer (rare)
Best for: Quick addition, no dissolving needed
How: Pour liquid cyanuric acid directly into pool with pump running. More expensive than
granular but dissolves instantly. Rarely available in stores.
How chlorine type affects stabilizer levels
🚫 Liquid chlorine & cal-hypo
No stabilizer added
These chlorine types don't contain CYA. You must add stabilizer separately and monitor levels manually.
⚠️ Trichlor tablets
Adds ~6 oz CYA per pound of tablets
Each 3-inch tablet adds stabilizer. Over a season, CYA can climb to 80+ ppm, requiring drainage.
⚠️ Dichlor granular
Adds stabilizer with each dose
Similar to trichlor. Monitor CYA monthly if using dichlor regularly. Switch to unstabilized chlorine if CYA exceeds 60 ppm.
✅ Salt chlorine generators
No stabilizer added
Salt systems produce pure chlorine without CYA. Add stabilizer once and rarely need to adjust.
💡 If using trichlor tablets, test CYA monthly. Once it reaches 60+ ppm, switch to liquid chlorine to prevent further buildup.
Pool stabilizer calculator FAQs
What is the ideal stabilizer level for a pool?
The ideal cyanuric acid (CYA) level is 30-50 ppm for outdoor pools. This range protects chlorine from UV degradation without reducing sanitizer effectiveness. Levels below 20 ppm allow rapid chlorine loss from sunlight (up to 90% in 2 hours). Above 80 ppm reduces chlorine effectiveness and may cause "chlorine lock."
How much stabilizer do I add to my pool?
To raise stabilizer by 10 ppm in a 20,000 gallon pool, add approximately 1.3 pounds (26 ounces) of cyanuric acid. The formula is: (pool gallons / 10,000) × (ppm increase / 10) × 13 oz = ounces needed. Dissolve granular stabilizer in a bucket before adding, or place in a sock in the skimmer.
Can stabilizer be too high?
Yes. Cyanuric acid above 80 ppm reduces chlorine effectiveness by binding too tightly to chlorine molecules. This condition is called "chlorine lock" — water may test high for chlorine but still grow algae because the chlorine is bound and unavailable for sanitizing. The only fix is to drain 30-50% of the pool and refill with fresh water.
Do I need stabilizer in an indoor pool?
No. Indoor pools without sunlight exposure don't need cyanuric acid. UV rays from the sun are what break down chlorine — without sun, stabilizer is unnecessary and actually reduces chlorine effectiveness. Indoor pools should maintain CYA at 0 ppm or very low levels (under 20 ppm).
How do I lower stabilizer levels?
The only way to lower cyanuric acid is to drain and refill with fresh water. Unlike other pool chemicals, CYA doesn't evaporate, degrade, or get consumed — it accumulates over time. To lower from 80 ppm to 40 ppm, drain 50% of pool water and refill. There is no chemical that removes or neutralizes CYA.
Do chlorine tablets add stabilizer?
Yes. Trichlor chlorine tablets contain about 50% cyanuric acid by weight. Each pound of tablets adds approximately 6 ounces of stabilizer to your pool. Over a season, this can raise CYA to 80+ ppm, requiring drainage. If using trichlor tablets, test CYA monthly and switch to liquid chlorine once CYA reaches 60 ppm.
How often should I test stabilizer levels?
Test CYA monthly during swimming season. If using unstabilized chlorine (liquid or cal-hypo), levels remain stable and rarely need adjustment. If using stabilized chlorine (trichlor or dichlor), test every 2-3 weeks as CYA accumulates quickly. Use CYA test strips or a test kit for accurate readings.
Does stabilizer affect my chlorine dosing?
Yes! Proper stabilizer levels (30-50 ppm CYA) help chlorine last longer, reducing how much you need to add. However, high stabilizer (over 100 ppm) can actually reduce chlorine effectiveness. After adjusting stabilizer, use our Chlorine Calculator to determine your new chlorine dosing requirements.