Help me understand CYA/FC and SWG

Brazillianguy

Member
Sep 5, 2021
11
Miami. FL
Pool Size
15000
Surface
Plaster
Chlorine
Salt Water Generator
Hi everyone,
I've been trying to put some concepts in my brain about CYA/FC and maintaining it with my SWG. So I currently understand that CYA helps to protect the chlorine in the pool from being used up by the UV of the sun. In my case, my pool is in constant sunlight. My CYA is <20 (the Taylor test doesn't even produce a cloudy solution). This means that even if I wanted to keep an acceptable FC range of 3-4 the sun will eat it all up in a few hours. Now increasing my CYA to, say 60-70 ppm, this will help protect the Chlorine from being completely removed from my pool. The down side to it is that CYA diminishes the sanitizing effects of the FC. In order to combat this I need to have a higher FC about 5. If I have my SWG running, won't I loose 1-3 ppm to the sun anyways? If without the CYA my SWG is needing (random number of 1-10) 9 on its level to maintain a 3ppm, will maintaining my CYA at 70 decrease the SWG setting (say 6 on 1-10 scale) to remain FC target at 5???? Thanks for helping with this concept.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,085
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Read these two wiki pages to understand how CYA creates active chlorine and reserve chlorine. CYA puts most of the FC in standby as reserve chlorine and releases it to become active as needed. That is the way the CYA protects the reserve chlorine so that it is available.

This chart illustrates the dynamics of the active chlorine (HOCL) versus FC (reserve chlorine). Youw ant to keep the HOCL between 0.010 and 0.1 for proper sanitation...

HOCl.gif



 
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Brazillianguy

Member
Sep 5, 2021
11
Miami. FL
Pool Size
15000
Surface
Plaster
Chlorine
Salt Water Generator
Read these two wiki pages to understand how CYA creates active chlorine and reserve chlorine. CYA puts most of the FC in standby as reserve chlorine and releases it to become active as needed. That is the way the CYA protects the reserve chlorine so that it is available.

This chart illustrates the dynamics of the active chlorine (HOCL) versus FC (reserve chlorine). Youw ant to keep the HOCL between 0.010 and 0.1 for proper sanitation...

HOCl.gif



So if the CYA holds the chlorine in “reserve” as the current FC is removed by UV exposure, does this reserve help replenish the loss to maintain the current FC level? (That’s the crux of my question?) thank you for replying
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
29,085
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
So if the CYA holds the chlorine in “reserve” as the current FC is removed by UV exposure, does this reserve help replenish the loss to maintain the current FC level? (That’s the crux of my question?) thank you for replying

No, your FC level will decrease.

You only need a small % of the FC for sanitation. However without CYA even though you have a FC of 3 and only need 0.1 ppm of HOCL for sanitation the suns UV will attack all 3 ppm of FC. With CYA most of that FC is shielded from the UV.
 

Brazillianguy

Member
Sep 5, 2021
11
Miami. FL
Pool Size
15000
Surface
Plaster
Chlorine
Salt Water Generator
No, your FC level will decrease.

You only need a small % of the FC for sanitation. However without CYA even though you have a FC of 3 and only need 0.1 ppm of HOCL for sanitation the suns UV will attack all 3 ppm of FC. With CYA most of that FC is shielded from the UV.
So then with CYA it will help preserve some of the FC? So it’s not that the only Chlorine that gets “shielded” is the one that is in reserve (attached) to the CYA.
With appropriate CYA, I shouldn’t see such drastic drops of FC and thus less work (lower setting needed) for the SWG?
 
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