Swimming Pool Water Disinfectant Series: Sodium Dichloroisocyanurate (SDIC)
Ensuring water safety is the core of public health management in swimming facilities. High-efficiency and stable disinfection technologies are the keys to achieving this goal. Sodium Dichloroisocyanurate (SDIC), also known as NaDCC or Dichlor, is a leading organic chlorine disinfectant. Due to its excellent solubility and ease of use, it has become a mainstream choice for pool disinfection.
What is SDIC?
SDIC is a white crystalline powder or granule with a slight chlorine odor. It is highly soluble in water and is available in powder, granular (common sizes: 8-30 mesh, 20-60 mesh), and tablet forms to suit different requirements.
Key Advantages
High Available Chlorine
The commonly used available chlorine contents of SDIC are 55%, 56% and 60%. Compared with liquid sodium hypochlorite (with only 5%-13% available chlorine), SDIC has a higher concentration of active ingredients, which means the cost of SDIC is greatly reduced under the same bactericidal effect.
Superior Solubility
SDIC has extremely high water solubility (about 25g/100ml at 25℃). In actual operation, SDIC can be dissolved fast when sprinkled into water. More importantly, it produces no precipitation or insoluble impurities after dissolution, which effectively protects the pool's filtration system and avoids filter material caking or pipeline blockage.
pH Neutrality
This is one of the core advantages that distinguish SDIC from other disinfectants. The pH value of SDIC aqueous solution is usually between 5.5 and 7.0, which is very close to neutral. When using sodium hypochlorite (strongly alkaline) or trichloroisocyanuric acid (TCCA, strongly acidic), acid or alkali must be frequently added to neutralize water quality, while SDIC has minimal interference on water pH, greatly simplifying the adjustment of chemical balance.
The Science of Disinfection: UV Protection
SDIC is highly regarded for outdoor pools because its molecular structure contains Cyanuric Acid.
The Problem with UV Rays
In outdoor pools, unstabilized chlorine (like liquid chlorine) is easily decomposed by ultraviolet radiation. Photons strike the hypochlorous acid molecules, breaking them down into chloride ions and oxygen, causing a rapid loss of disinfecting power.
The Stabilizer Barrier
When SDIC dissolves, it releases both hypochlorous acid and cyanuric acid. The cyanuric acid forms a weak chemical bond with the free chlorine, acting as a "shield" against UV damage. This combined state can effectively prevent the damage of ultraviolet rays to chlorine molecules, significantly prolonging the half-life of chlorine in water and reducing the frequency of chemical replenishment.
Application and Usage Scenarios
Because SDIC dissolves so quickly, it is best suited for manual dosing rather than slow-release chemical feeders. It is usually dissolved in a bucket first and then spread evenly across the pool surface.
Indoor Swimming Pools
Focus on controlling cyanuric acid concentration to avoid accumulation; strengthen ventilation to reduce indoor chloramine concentration and avoid the accumulation of pungent odor.
Outdoor Swimming Pools
Focus on cyanuric acid management; appropriately increase cyanuric acid content to stabilize chlorine efficiency due to strong UV radiation in summer, but conduct regular monitoring to avoid exceeding the standard; timely add disinfectant after rain and clean impurities brought by rainwater.
Children's Exclusive Pools
Children's skin and mucous membranes are more sensitive, so the residual chlorine concentration must be strictly controlled; increase the frequency of cyanuric acid detection and change water in time when the concentration exceeds the standard.
SDIC is very suitable for use in swimming pools with plastic liners, acrylic plastic or fiberglass saunas. The temperature of saunas and Spas is high, leading to rapid chlorine volatilization. Some service providers do not recommend using SDIC or TCCA in saunas, but SDIC is still the most important disinfectant for saunas and Spas.
Comparison with Other Disinfectants
| Feature | SDIC (Dichlor) | TCCA (Trichlor) | Bleaching Water |
|---|---|---|---|
| Available Chlorine | 55% - 60% | 90% | 5% - 13% |
| Impact on pH | Slight Decrease | Decrease | Increase |
| Skin Irritation | Low | Low | High |
| Stability (Dry) | Excellent | Very High | Poor (volatilizes) |
| Shelf Life | Long | Long | Very Short |
You may like: Swimming Pool Water Disinfectant Series: Trichloroisocyanuric Acid (TCCA)
Troubleshooting Common Issues
| Problem Phenomenon | Core Causes | Solutions |
|---|---|---|
| Poor disinfection effect and continuously low residual chlorine |
1. Insufficient dosing amount; 2. Excessively high cyanuric acid concentration (chlorine lock); 3. pH value deviating from 7.2-7.6 range; 4. Circulation system failure leading to uneven diffusion of disinfectant |
Regularly detect cyanuric acid concentration and reduce it by refreshing pool water when exceeding the standard |
| Pungent odor in water | Combined chlorine concentration is too high. |
It is necessary to increase the residual chlorine concentration to 5-10 mg/L for chlorine shock. |
| White residue after dosing of dosing pipelines | Large amount of dichlorine added directly to pipeline. | Control dosage within a reasonable range. |
