CTX-400 Chlorine Stabilizer

If the chlorine in your pool disappears quickly during the summer months, even with regular treatments, the most common cause is degradation caused by ultraviolet rays from the sun. CTX-400 Chlorine Stabiliser for swimming pools (ClorProtect) is a granular cyanuric acid stabiliser developed to extend the disinfecting action of chlorine in outdoor pools, reducing losses caused by solar radiation. Available in a 4.5 kg pack, it is suitable for all types of residential outdoor swimming pools.

What is CTX-400 ClorProtect Chlorine Stabiliser

CTX-400 ClorProtect is a granular chlorine stabiliser, white in colour, whose active ingredient is cyanuric acid (isocyanuric acid). This compound acts as a protective shield for free chlorine in the water, binding to chlorine molecules and making them less vulnerable to photodegradation caused by ultraviolet rays. The result is water that stays disinfected for longer periods, with lower chlorine consumption throughout the season.

Ideal for: outdoor pool owners who use hypochlorite or salt electrolysis and notice a rapid drop in free chlorine during the months of highest sun exposure.

How CTX-400 chlorine stabiliser works

Without a stabiliser, solar radiation destroys available chlorine very rapidly. According to the manufacturer’s technical datasheet, in a pool exposed to strong sunlight without CTX-400 ClorProtect, 90% of the total available chlorine is lost within just 3 hours. By adding 4 kg of CTX-400 per 100 m³ of water, that loss is reduced to just 30% over the same period – meaning chlorine remains active for much longer.

Designed for those who want to keep their water disinfected without topping up chlorine every day, CTX-400 cyanuric acid for swimming pools acts as a photochemical buffer: it protects chlorine from UV rays and helps maintain a more stable chlorine reserve, provided the cyanuric acid level stays within the recommended range. The result: less chemical consumed and more stable water throughout the week.

How to apply CTX-400: dosage and directions for use

The initial dosage recommended by the manufacturer is 4 kg of CTX-400 per 100 m³ of water, which is equivalent to 40 ppm of cyanuric acid. This dose should be applied at the start of the season, with the filtration system running.

Application method: introduce the dose of CTX-400 ClorProtect into the skimmers or the pump pre-filter, with filtration active. This ensures the product is distributed evenly throughout the pool water.

After the initial application, the aim is to maintain the cyanuric acid level between 30 and 60 ppm, and it must not exceed 75 ppm. Above that value, the disinfecting effectiveness of chlorine can be compromised and partial replacement of the pool water with fresh, unstabilised water will be necessary.

Which types of pool is CTX-400 suitable for

CTX-400 Chlorine Stabiliser is suitable for outdoor swimming pools, both in-ground and above-ground. It is compatible with all common pool finishes: mosaic tile (gresite), liner, and polyester. The granular formulation suits pools of all shapes and sizes, and is equally appropriate as a supplement for salt electrolysis systems or for treatments using unstabilised chlorine.

Compatibility and precautions: salt water, liner, and polyester

CTX-400 ClorProtect is compatible with salt electrolysis pools, working as a complement to the chlorine produced by the salt system. In pools with a liner or polyester finish, it is recommended to pre-dissolve the product in water before adding it to the pool, to avoid direct contact between the granules and the pool surface.

Under EU classification (Regulation (EU) No 1272/2008), the product is not classified as hazardous. Even so, it should be stored in a dry place and kept out of reach of children. If the cyanuric acid concentration exceeds 75 ppm, partial replacement of the pool water with fresh water containing no CTX-400 is required. The product is intended exclusively for outdoor swimming pools.

Maintenance: recommended levels and when to reapply

After the initial season start-up dose, the cyanuric acid level should be monitored regularly using test strips or an analysis kit. The recommended maintenance range is between 30 and 60 ppm, and must not exceed 75 ppm. Below 30 ppm, UV protection for chlorine is insufficient; above 75 ppm, the disinfecting effectiveness of chlorine can be compromised and the pool water will need to be diluted.

Cyanuric acid does not break down with normal use – unlike chlorine, it is not consumed by solar radiation. Reapplication during the season becomes necessary mainly when there is significant water replacement, for example after backwashing the filter, partial draining, overflow, water loss, or heavy rain that requires topping up the pool.

Frequently asked questions