Chlorine/CYA Chart question

melbajr

LifeTime Supporter
Aug 10, 2013
54
Florence, SC
#1
On the SWG chart the asterisk at CYA of 60 says 'Not recommended' has me confused :?. To me it seems that if it is not recommended at 60 because it's too high then why are 70 and 80 okay? Also, why are there no listings for lower CYA levels. I'm sure some of you are laughing :lol: right now because I'm sure I've misread or misunderstood some part of that page (or all of it) and that's okay. But please help me to see what I missed.
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
41,197
Tucson, AZ
#2
In the SWG chart, 60ppm has an * because it is lower than we typically recommend for SWG pools and that is also why the SWG table does not go lower.

For a SWG, the minimum FC level is 5% of the CYA level.
For a non-SWG pool, the minimum FC level is 7.5% of the CYA level.
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,087
Franklin, NC
#3
You are not reading it wrong, because we recommend 70 - 80 for CYA on a SWCG pool.

It may seem counter intuitive, but the higher CYA allows the SWCG to work less. Here is a quote from an old post that explains it better than I can

Despite what a great deal of the available literature says, higher CYA levels reduce the total amount of chlorine required to sanitize your pool. Even though a higher CYA level requires a higher FC level, the amount of chlorine you need to add each day to maintain that higher FC level is actually lower than what you would need at a lower CYA and FC level. This happens because CYA protects FC from sunlight, reducing the amount lost to sunlight enough to more than make up for the higher FC levels required.

Since less total chlorine is required at higher CYA levels, the SWG cell doesn't need to run as long each day. Since the cell in a SWG has a lifetime based primarily on how long it is on, a lower daily run time results in longer cell life.
 

Isaac-1

TFP Expert
LifeTime Supporter
May 10, 2010
6,711
SW Louisiana
#4
We should probably note that some SWG manuals suggest running at a CYA level of 40 ppm, doing so just means you will loose that much more chlorine to sunlight, particularly in sunbelt states requiring the SWG to run for more hours per day, and therefore shortening the life of the SWG cell. In other words running at 40 ppm CYA is better for the manufacturer as they get to sell you a replacement cell more often. Our 70-80 ppm CYA suggestion is a trade off between maximizing SWG cell life while still maintaining a low enough CYA that SLAM process to clear up an algae bloom should one occur is still a practical option.
 

melbajr

LifeTime Supporter
Aug 10, 2013
54
Florence, SC
#5
Thanks to all for that great info!! :angel: :angel: :angel: Y'all are angels!
I'm understanding the chlorine/cya chart now. Before I was doing what it said but confused as to why. So thank you again! KNOWLEDGE IS POWER & TFP GIVES POWER TO THE PEOPLE!!!:whoot:
:lovetfp::party:
 

kimkats

Mod Squad
LifeTime Supporter
Jul 10, 2012
35,556
Tallahassee, FL
#6
Thanks to all for that great info!! :angel: :angel: :angel: Y'all are angels!
I'm understanding the chlorine/cya chart now. Before I was doing what it said but confused as to why. So thank you again! KNOWLEDGE IS POWER & TFP GIVES POWER TO THE PEOPLE!!!:whoot:
:lovetfp::party:
This post makes me SMILE! :sunny:

Kim :cat: