Cya/Chlorine relationship

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Abaker6468

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Jun 8, 2016
66
Mechanicsburg, PA
Sent an email to APSB (American Pool and Spa Builders) about why Hayward was telling me to keep my SWG cya level 30-50. Response is below. Any comments appreciated since this makes things even more confusing lol.

"I heard back from Hayward and was told that the contradictory responses may be due to the fact that the CYA levels have been revised over the years from 60-80ppm down to 30-50ppm. Some dealers may still be unaware of the change. The lower CYA levels came about from the more recent understanding by CDC and others of the impact of CYA on chlorine's effectiveness. The recommended CYA level is a SWG pool is no different than a non-SWG pool. Hayward does not modify CYA levels based on geography (e.g Pennsylvania v. Arizona v. Minnesota). CYA levels for INDOOR POOLS are recommended to be ZERO as it presumed that these receive no direct sunlight. I hope this helps with your questions."

Thank you,


17,200 in ground pool, DE filter,3/4 hp pump, solar heater, SWG (Hayward Salt and Swim 3C). 1988 Hot Springs Highlife-K Hot Tub (415 gal.)
 
Manufacturers know that their cells are more efficient at the higher CYA level - i.e. more chlorine from a few less watts, so they used to recommend it and some still do. The reason why is not fully understood, it's just a known observation, and it's slight.

But at the end of the day, it's not in their financial interest for the cell to run longer, so internally, any discussion/debate would be won by the bean-counters over the engineers. That is, for a business, why say anything different from a regulatory body unless they can make more money from it.

For the owner, the higher CYA allows for less SWG run-time, and that's why it's recommended here at TFP. Less run time = longer cell life and less rapid pH rise, which means less frequent MA additions.

It's purely a cost/convenience issue. You can run safely at 50 if that's what you prefer. And 80 won't hurt the cell (quite the contrary) so you can do that if you like. TFP recommends 70/80 ppm CYA for outdoor residential pools because it is right for SWG, not because it's politically correct.

As far as indoor pools, there are very good reasons to use CYA, primarily the softening of the "harsh" part of chlorine and maintaining a reserve for varying bather load. But like everything else on this topic, regulatory bodies are not doing the yards they should be doing to get this right.

TFP and particularly a few very dedicated chemists have done that work and made the regulatory bodies aware of it. Again, the regulatory bodies don't care about the opportunity for improved public safety and water conservation.
 
By the way, it's a very, very good question! And nice to meet you via TFP. You can probably tell this whole thing kinda peaves me off! :)

I must have spent 50 hours of reading to understand, yet it's a simple thing and has been well understood for 40 years. Bureaucrats would be able to grasp the importance and mechanisms of the CYA-FC relationship if they wanted to.
 
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