Any reason to add CYA when levels are low but chlorine readings are fine?

PatD25443

New member
Jul 30, 2021
4
Shepherdstown WV
Hi all. I'm a new (one season) owner of a 20k pool with a SWG. I just replaced the cell with a 40k capacity one. Until recently I couldn't get a free chlorine reading to save my life. I finally realized it had to be CYA so I got a test strip and it showed I had virtually none. I added four pounds of CYA over the course of a couple of days, and ever since I've been getting free chlorine readings well within the normal range (around 2). All of my other readings are within the good range as well -- except, that is, CYA, which still reads low even after the 4 pounds.

I've been experimenting running the SWG at 50 percent for 10-12 hours a day and now consistently getting free chlorine readings around 2. For what it's worth, the pool gets pretty light use and always looks perfectly clear and clean.

Here's my question: if I'm now getting consistently acceptable free chlorine readings, do I really need to keep adding CYA? I've read that too much can eventually be a problem and require draining your pool, which I don't want to do.

Thoughts? Thanks.
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
5,150
NW Ohio
Test strips are notoriously unreliable and making any decisions based on what you read from them is a shot in the dark. We can't make any comments or suggestions based on them.

So the first step to any of this is to get reliable numbers to base your decisions on. That means doing your own testing with a good kit, Test Kits Compared. I recommend the TF-100 or Taylor k-2006.
 

PatD25443

New member
Jul 30, 2021
4
Shepherdstown WV
Thanks. I understand what you're saying and that test strips are unreliable. It can't just be a coincidence that after weeks of not being able to get any kind of FC reading I add 4 pounds of CYA and all of the sudden I'm consistently getting a reading of 2? I'm also confused because everything I've read says that 1-3 is the acceptable range for FC for a private pool. That's not right?
 

PoolGate

Gold Supporter
TFP Guide
Jun 7, 2017
6,478
Damascus, MD
Pool Size
29000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
With no CYA your free chlorine will be gone in as little as hours in the sun. CYA buffers and acts as a sunscreen to chlorine. So any CYA will have a noticeable effect on chlorine life. This site has a specific, proven, and scientific approach to pool care and recommended chlorine levels. Read pool school and enjoy the site as many others have.
 
Last edited:

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,358
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
everything I've read says that 1-3 is the acceptable range for FC for a private pool. That's not right?
FC level is based on your CYA level. It is a % of CYA. See FC/CYA Chart

It is true you are getting a FC level to sustain now because you added CYA. But that FC level has to be high enough to keep the pool clean and sanitary, based on what the CYA level is.

Please complete your signature so we know what pool size, type, equipment you have so we can help you better.
 

woodyp

Mod Squad
TFP Expert
LifeTime Supporter
Apr 17, 2010
11,389
East Texas
That FC/CYA chart recommends 70 to 80 CYA to help maintain a lower chlorine residual on a constant and consistent basis. I'd raise that FC level output to 4 after adjusting cya.
 
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