Hi All,

Here is a link to a great paper on a study of CYA.

http://www.ppoa.org/pdfs/PrP_Cyanurics% ... 20Bomb.pdf

the upshot is, keep it as low as you can.

Anything over 70ppm, and you can throw TONS of money away in chlorine that will not be effective.

After reading all this, please just do as much of a water change as you can afford (100%)? and stop banging your head against a flagstone.

While there is some good information in that paper, many of the conclusions are wrong compared to the modern understanding. The effects of CYA have been misunderstood for decades. That paper corrected some of the misunderstandings from back then. But new information continues to come in and we now know that parts of that paper are based on newer misunderstandings of what happens with CYA. It is also interesting to note that the author of that paper has ties to the ORP sensor industry. ORP sensors are known to have problems with high CYA levels that are unrelated to what happens in actual pools.

Higher levels of CYA require additional FC to maintain the same active sanitizer level as lower levels of CYA. But even once this is taken into account, higher levels of CYA continue to reduce the amount of chlorine lost to sunlight, contrary to the graphs shown in that report. As the CYA level increases various other problems do start to become significant. It is generally agreed that above a CYA level of 80 or 90 the problems are more significant than the chlorine savings. Still it is possible to run at higher levels, several people here have run their pools with CYA levels higher than and while they did have some significant issues the behavior was nothing like what is described in that paper.

While that paper does have some good points it deals mostly with using CYA in commercial pools that use ORP controllers and not manually chlorinated residential pools or pools with SWGs. Aslo, the person who wrote the paper has a hidden agenda since he was connected with one of the major ORP conroller manufacturers.

Jason, do you have some links that explain the modern understandings? Interesting subject...

Off subject, but how do you get the "Quote" to say something else? Like when Jason quoted "Lershac" it says "Lershac wrote:".

I turned the code off for the quote above, and you can see that it says quote="benavidescj". Whatever is in the "" will display as the identifier, like this




It's filled in automatically if you select quote instead of reply.

benavidescj, there isn't a good overview that is easy to read that I know of. If you really want to get into the subject, check out this topic, just keep in mind that that topic gets very technical very quickly.

I think an easier to understand summary of the "Chlorine/CYA Relationship" is in the section of that name in this post. That section has a bit of the history as well as links to scientific papers and other technical threads so you can dive as deep as you want to go -- just remember that there is no lifeguard here in The Deep End.