Stabilised chlorine granules that dissolve fast for instant top-ups and pH-neutral shocks. SDIC adds 1 ppm of free chlorine per 1.4 g per 1000 L without raising pH.
Standard dose adds 1 ppm. For a 5 ppm shock multiply by 5. For a fresh fill establishment, dose 5-10 ppm and run circulation for 4 hours.
Sodium dichloroisocyanurate dihydrate (SDIC), supplied as fast-dissolving granules with at least 56% available chlorine and built-in cyanuric acid stabilisation.
SDIC dissolves to release hypochlorous acid (the active sanitiser) and cyanuric acid (the stabiliser). Unlike TCCA, the granules are pH-neutral, so balance is preserved while sanitiser is added or shocked. The cyanuric acid binds reversibly to chlorine and protects it from UV destruction.
Daily chlorine top-ups must not destabilise pH. SDIC is the standard pool-grade granule for that job. Its fast dissolution makes it ideal for shocks too, where speed and pH stability both matter.
1.4 g per 1000 L raises free chlorine by 1 ppm.
Yes. SDIC is the pH-neutral chlorine donor used worldwide for daily dosing.
Wait until free chlorine drops below 5 ppm; usually 60 minutes after a top-up.
Around 6-12 months of weekly maintenance for a 1500 L hot tub.
Yes. The granules supplement salt chlorination during heavy bather load.
Yes. Dose 5 ppm of free chlorine for a routine shock or 10 ppm for a heavy shock.
Sodium dichloroisocyanurate dihydrate (SDIC) at >= 56% available chlorine.
The dichloro-cyanurate ion is balanced between acidic and basic groups, so pH stays in band as the granules dissolve.
Yes. Each 10 ppm of free chlorine added by SDIC adds approximately 6 ppm of cyanuric acid.
High combined chlorine; shock at 10 ppm and run circulation for 4 hours.
Dose was added neat or pH out of band; rebalance and clean filter.
Switch to calcium hypochlorite for shocks; refresh part of the water if CYA above 80 ppm.
SDIC is fast-dissolving, pH-neutral granules for daily and shock dosing. TCCA is slow-release, acidic tablets for low-effort dispensing.
SDIC is stabilised and gentle on pH. Calcium hypochlorite is unstabilised, faster acting, and raises pH; better for indoor pools and CYA-saturated water.
How the three main hot tub sanitiser families compare for everyday use, hot water performance and running cost.
| What matters | Chlorine | Bromine | Chlorine dioxide |
|---|---|---|---|
| Best for | Fast, low-cost everyday sanitising | Hot tubs and spas that want a steadier, milder feel | Deep cleans, biofilm removal and problem water |
| Ideal level | 3 to 5 ppm free chlorine | 4 to 6 ppm total bromine | Used as a clean-up dose, not a daily residual |
| Performance in hot water | Burns off faster at spa temperatures | Stays effective in hot water | Used as a strong clean-up dose, often chosen for biofilm problems |
| pH sensitivity | Works best at pH 7.2 to 7.6 | Effective across a wider pH range | Largely unaffected by pH |
| Odour | Noticeable when chloramines build up | Milder than chlorine | Low odour at normal clean-up doses |
| Typical running cost | Lowest day to day | Slightly dearer than chlorine | More per dose, but only used occasionally |
| ClearSpa products | Stabilised chlorine granules and mini tablets | Bromine tablets 20g and bromine granules | Chlorine dioxide |