FC/CYA Chart Recommendations seem high?

[fredricr1]

All,

I've read on TFP that the ideal FC level should be roughly >=7.5% of CYA (e.g., FC = 6, CYA = 80, 6/80 = 7.5). I've also read in a few threads that the sanitation effectiveness is the same regardless of the FCppm as long as it's in the same ratio (e.g., 3/30 = 5/50 = 7/70) but as CYA goes up other problems, such as higher chlorine costs and prohibitive SLAM requirements.

So...why does the FC/CYA chart (for SWG pools) need CYA to be up in the 60,70,80 range? If I set my CYA to 30 and maintain FC at 3, I'm over that effective ratio and should have good sanitation with reduced chlorine production from the SWG, right? I appreciate some clarification and I apologize if this has been addressed in other threads - I've read a few and didn't get this question quite answered. It just seems that if we can get a clear pool at consistently lower levels, costs go down.

Thank you.

 

[ajw22]

All,

So...why does the FC/CYA chart (for SWG pools) need CYA to be up in the 60,70,80 range? If I set my CYA to 30 and maintain FC at 3, I'm over that effective ratio and should have good sanitation with reduced chlorine production from the SWG, right? I appreciate some clarification and I apologize if this has been addressed in other threads - I've read a few and didn't get this question quite answered. It just seems that if we can get a clear pool at consistently lower levels, costs go down.

Thank you.

To get down into the weeds of the chemistry I suggest you review Pool Water Chemistry

Salt Water chlorine Generation (SWG) pools seem to require a higher level of CYA, about 70-80 ppm, to operate efficiently. The theory is that the CYA is slow to "store" the chlorine as it is being generated so without enough CYA there is a build-up of chlorine that degrades the performance of the salt cell. I would prefer that the SWG manufacturers offer a larger lower-power (per length) cell that would work efficiently at lower CYA concentrations.


and specifically post #5 CYA and Lifetime of Chlorine in the thread.

Also FC - Concept of "Reserve"

 

[getreal720]

Although it seems your post is from a point of view in running a SWG (and I'm not) this is something I've been giving a lot of thought over the past few days.

I would not say that having a higher CYA level causes you to really "spend" any more money on chlorine. It's just that you need to maintain a higher level of chlorine. So if there were really any increased costs, it should only be upfront after raising your CYA level and perhaps a tiny bit when you SLAM the pool.

You may have double the chlorine in the pool, but you also have double the CYA to protect it. The "demand" of chlorine from your pool shouldn't change all that much. Although it's a bit more into the deeper end of chemistry science, there is a bit of an argument that having more CYA and more chlorine in the pool can actually reduce the demand from your pool.

I'm "somewhat" knowledgeable about the science, but I've been spending a good bit of time reading and researching trying to get a grasp on the referenced post by chem geek.

The science does make specific points about running a SWG with higher CYA levels and in having those higher CYA levels, your SWG runs more efficiently and your not losing a bunch of FC to sunlight since there is ample CYA to bind it.