Cya in SWG pool


Well-known member
Jun 14, 2018
Is there any “negative” (other than “wasting “ LC to maintain target FC) to keep a lower cya in a SWG?

Im around 40 cya in my SWG and everything seems to be fine. Is it worth adding another 30 ppm or am I ok doing what I’m doing?

I also tend to be more conservative and treat the pool like it’s a non SWG and then some — keeping the Target FC around 8 ppm which is about 20% of cya. I just like to have plenty of buffer.

Is there any issue with this?


Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
No. Just uses up the SWCG faster.

Just be sure your SWCG can create chlorine fast enough in the middle of the day to outrun the loss to the sun with the lower CYA. Test your FC on a really sunny day at different times during the day to see what the characteristics are.


Well-known member
Jun 14, 2018
Thanks. Today is very sunny so I’ll experiment. But what if I supplement with LC? (Small amounts to constantly maintain?) I also have the SWG on 100%. Not sure if that’s bad too...

not sure how much longer the SWG will last. Was installed when the pool was built in 2014.


Well-known member
Jun 14, 2018
Was at around 9 fc at 7 A.M. and around 7 fc at 1 PM...sun has been beating down and high 80’s. So I guess I’ll just leave the SWG at 100%.

But my cya is 40 - just added another sock so maybe will go to 45-50, but will like to stay around 8 ppm, so will add just a tad LC. I know that’s high for a SWG but makes me more comfortable.

So, nothing wrong with this approach?

ant 83

Well-known member
Nov 3, 2015
appleton wisconsin
Your cya loss rate will be higher than others who maintain a lower fc target than you, due to oxidation from the chlorine.

Degradation of Cyanuric Acid (CYA))

So, assuming a CYA loss rate of around 0.4 ppm/day in our pools this comes to 12 ppm per month which is clearly enough to be noticeable as the months pass during a swim season. If one shocks the pool, then the rate of loss could be about 2-3 times faster.

Wojtowicz also shows a strong temperature dependence on the chlorine oxidation of cynauric acid where every 10F increase in temperature results in roughly doubling the rate of degradation. So his data was with pools at 85F so pools at 90F could have degradation rates about 1.4 times higher.


Gold Supporter
Sep 26, 2016
Why don't you just add some more CYA, I added some last week and this week to get mine back up to 70. Amazon has a Clorox brand that dissolved very easily for me, Wal-Mart carries it also its cheap. 60 isn't "recommended" so I figure not take any chances. If you want to lower your SWG % you can run the pump time longer, I have been experimenting with that also.


LifeTime Supporter
Jul 12, 2008
Seacoast, NH
Your SWG from 2014 may have plenty of life left in it. Mine is from 2008 and is still going strong. I know mine is at the outer limits of life expectancy, but I’d hate for you to think yours is on its last legs if it isn’t.