Stabiliser calculator: how much cyanuric acid to add?
Stabiliser protects chlorine from the sun, but too much locks it up. Enter the volume and your measured level to find the amount to add up to target — without crossing the point where chlorine stops working.
Result
Stabiliser to add1.5kg
Stabiliser dissolves slowly: place it in the skimmers or a basket, with filtration running, and retest after 24 to 48 h.
Check your product label: some are not pure cyanuric acid and are dosed differently.
How this calculation works
This calculation applies the standard dilution rule for cyanuric acid:
Stabiliser (g) = Volume (m³) × (target level − measured level), in mg/L.
For pure cyanuric acid, 1 g per m³ raises the level by about 1 mg/L (ppm). Going from 10 to 40 mg/L in 30 m³ therefore takes 30 × 30 = 900 g. The ideal range is 30 to 50 mg/L: below 20, chlorine degrades too fast in the sun; above 70, it becomes locked and stops working.
Frequently asked questions
What is the ideal stabiliser level?
Between 30 and 50 mg/L. Below 20 mg/L, chlorine is destroyed too quickly by UV; above 70 mg/L, it becomes ineffective even at the right dose.
What if the stabiliser is too high?
There is no product to bring it down: the only lasting fix is to renew part of the water. Then prefer an unstabilised chlorine to avoid making it worse.
Does stabiliser get used up?
Very little: it mainly drops through dilution (water renewal, rain, splash-out). It tends to build up with stabilised chlorine, which is why it needs monitoring.