Quote Originally Posted by jawman
Carl,

Can you please explain the math? I'm struggling to understand this stuff too. Also trying to figure out how the CYA of 5ppm figures into the equation. For example, if the CYA were 10ppm, would you advise Lorretta to put in the same amount of Chlorine?

Thanks,

jawman

He is taking those numbers off the "Best Guess" chart. http://www.poolforum.com/pf2/showthread.php?t=365

CYA is stabilizer. It makes CL stable in water. So the more Cyanuric Acid (CYA) there is in the water, the more free CL you need to kill bacteria. As you can see from the chart linked above, the more CYA, the more free CL you would have.

As a side note, most people recommend a CYA level of 30, but I ran mine last year at 60+ with no issues and no algae. That was not intentional (I mis-measured...) but it worked out just swell. All I had to do was keep my FC at 9-10. My water was so clear it hurt to look at it.