Guest Column - October 2013
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CYA: Too Much of a Good Thing?
Risks With Over-Stabilization of Chlorine

By Stanley R. Pickens, Ph.D.

Keeping CYA levels below 50 PPM may be quite challenging for facilities routinely using stabilized chlorinating agents, chlorination compounds that contain CYA. (These stabilized chlorinating agents are more technically known as chlorinated isocyanurates.) Some examples are trichloro-s-triazinetrione (trichlor) or sodium dichloro-s-triazinetrione (dichlor). Trichlor adds 0.6 PPM of CYA for each PPM of free chlorine it contributes. Dichlor adds 0.9 PPM of CYA per PPM of chlorine. All this CYA—coming in like stowaways on the chlorine—can quickly add up. For instance, in a pool that receives a 5 PPM daily dose of chlorine, all in the form of trichlor, and has up to a 2 percent water replacement per week (filter backwash), the CYA level in the water would build from zero to 50 PPM in less than three weeks. The only practical way to remove the CYA is to drain and replace water. Such increased water replacement is at odds with the growing pressure to conserve water in a large number of regions.

This all leads to the following recommendations, which will help you to prevent the chlorine you rely on from being shackled to excessive CYA:

  • Use CYA (stabilizer) only when it is needed to protect chlorine against bright sunlight. Neither CYA nor stabilized chlorinating compounds (chlorinated isos) should be used on indoor pools, or on spas or spray pads.
  • Avoid the use of stabilized chlorine on pools with high chlorine demand. Add the stabilizer separately, only when needed, to avoid excessive CYA concentrations.
  • Test CYA levels regularly to ensure that they are in a reasonable range.

Chlorine stabilizer can be useful, or even necessary, to protect chlorine against bright sunlight. But adding CYA to a pool is a bit like adding a strong seasoning to a gourmet recipe: The fact that a little may be good does not equate to a lot being even better.

Stanley Pickens, Ph.D., is a senior research associate for Axiall Corporation's Water Treatment Products Group. He has a Ph.D. in inorganic chemistry, is a member of the Association of Pool & Spa Professionals' Recreational Water Quality Committee, and has worked with various other advisory councils on specific assignments. He has presented lectures at various venues on topics related to disinfection and water treatment. In addition, he is an inventor with 19 U.S. patents.