Why it matters
Without CYA, outdoor FC burns off in 2 to 4 hours. Too much CYA suppresses chlorine effectiveness and the only fix is partial drain.
Ideal ranges
| Water type | Ideal | Acceptable |
|---|---|---|
| Outdoor chlorine pool | 30 to 50 ppm | — |
| Salt chlorine pool | 60 to 80 ppm | — |
| Indoor pool | 0 ppm | — |
| Spa | 0 to 30 ppm | — |
- Salt chlorine pool: Higher because SWG runs more chlorine through cell.
- Indoor pool: No sun, no need for CYA.
How to test
- 1
Turbidity test (Taylor K-2006 includes one)
Pour reagent and pool water into the tube until the dot disappears. Read CYA on the side.
How to correct low cyanuric acid
Add granular CYA via skimmer
Slow to dissolve. Takes 5 to 7 days to register fully. Do not over-add.
How to correct high cyanuric acid
Partial drain and refill
The only reliable way to lower CYA. Drain 25 percent, refill, retest.
Reverse osmosis pool service
If draining is impractical (high water table), some areas have RO trucks.
Common causes
- •Trichlor tabs add CYA every time they dissolve
- •Stabilised dichlor shock adds CYA
- •Long pool service intervals letting trichlor build up
FAQs
What is the FC/CYA ratio?
FC must be at least 7.5 percent of CYA for sanitation. 60 ppm CYA needs 4.5 ppm FC minimum.
Why did my CYA spike?
Trichlor tablets and dichlor shock both contain CYA. Switch to liquid chlorine to avoid this.