High CYA, lower effectiveness?

[mikeconnor]

Split by moderator from HERE. jblizzle

I had a pool that I worked on that had an 80 CYA and very high chlorine level. Even with the salt gen off the chlorine level refused to drop. I had to drain water to re-balance the water. Had no idea it stopped bacteria reduction effectiveness. Great site here!

 

[chem geek]

Re: This Article Claims Cyanuric Acid Chlorine Lock is a Myth

If the chlorine level was high, then that overcomes the high CYA level with regard to bacteria reduction effectiveness. The active chlorine level that determines the pathogen kill rate is proportional to the FC/CYA ratio. So if you raise the FC proportionately as the CYA level rises, then you get the same pathogen kill rates and oxidation rates from chlorine. You can absolutely operate a pool at 80 ppm CYA and in fact that is generally the recommended level for SWCG pools in order to reduce the losses of chlorine to sunlight. The only issue with the higher CYA level is that it increases the risk, particularly in manually dosed pools that have greater FC swings, that the FC/CYA ratio gets too low and algae can then grow. It would then take a higher SLAM chlorine level to kill off the algae. See the Chlorine / CYA Chart.

 

[mikeconnor]

Re: This Article Claims Cyanuric Acid Chlorine Lock is a Myth

Thank you.....what prompted me to act was that the place that I was having my water tested at the time was very concerned about the high 6 chlorine level and I was getting a white sediment on the liner above the water line. The owner used to just dump shock in the pool as she was paranoid about germs. It was frustrating.

The thought was that the high CYA reading was stopping the high chlorine level from coming down even though the SG was off. I may have been as high as 100 above the 80 I quoted above.

Thank you for the link lll check it now. MIKE

 

[chem geek]

The higher CYA level will slow down the rate at which chlorine breaks down in sunlight, but the FC/CYA ratio determines how quickly the chlorine will drop from reaction with pool covers or ammonia and organics in the pool (i.e. bather load, blown-in leaves and pollen, etc.). If the pool was fairly clean and didn't get a lot of sunlight, then the chlorine drop rate can get pretty slow. Water temperature also plays a significant role where colder water slows down all chemical reactions.