Should I raise my CYA level?

plucky71

LifeTime Supporter
Apr 18, 2010
116
Michigan
I'm trying to figure out this CYA level thing. Right now my CYA is at 35. It is within specs recommended on this site. But I do get direct sunlight from sun up to down, so maybe I should have it higher as it is recommended for full sunlight?

And I am also wondering about chlorine use in regard to efficiency. With higher CYA my target FC raises. But does that mean that with higher CYA the FC used by the pool will decrease or change at all?

So should I raise my CYA, and if yes what is the benefit?

Here are my current test results:

FC 7
CC .5
pH 7.4
T/A 70
CH 250
CYA 35
Temp. 84

Thanks for the help! :goodjob:
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
Your CYA level is fine where it is for now, but it will tend to drift down over the course of the swim season. Since you want it to be at least 30 at the end of the season, you will need to raise it at some point, and now is as good a time as any. The normal approach is to raise CYA to 50 in the spring, so it will still be at least 30 in the fall.

Higher CYA levels require a higher FC level, but you actually need to add less total chlorine to maintain that higher level because the higher CYA level protects the chlorine from sunlight more effectively. The disadvantage is that higher CYA levels make it more difficult to fight algae, though this is not a big deal in the 30 to 50 range, it becomes important as CYA goes above 50.
 

svenpup

LifeTime Supporter
Nov 18, 2009
835
Sacramento, CA
The appropriate CYA level is a balance between sun protection and chlorine effectiveness.

With CYA too low, the sun will burn off enough chlorine during the day that FC falls below minimum (or maybe even to zero).

With CYA too high, it becomes difficult to shock because of the high FC level needed.

The guideline CYA levels here are high enough to protect FC from the sun and ensure residual sanitizer in the water throughout the day, but not so high that shocking is impossible.

What level you chose within the guideline range is a judgement call based on your pool specifics including amount of sun exposure, and latitude.

If your overnight loss is acceptable (<1.0) but you find that you are losing a lot of FC throughout the day you can raise the CYA. You should find that with higher CYA you lose less FC throughout the day and your overall chlorine demand may go down even though your target level is higher.

The downside if you go too high is if you ever let the FC drop below minimum and algae does take hold you will have extremely high shock levels and shocking will be difficult.
 

plucky71

LifeTime Supporter
Apr 18, 2010
116
Michigan
Thank you both for the excellent and helpful answers. That does give me a better understanding of the Chlorine/CYa relationship. I think I will raise my CYA level now, or over a period of time. I have two bags of shock plus, which I believe are di-chlor. I would like to use them up and get rid of them. Can I slowly use them to maintain my FC level and at the same time raise my CYA level? For example, add 1/4 or 1/8 of a bag, circulate, test FC and repeat the next day.
 

svenpup

LifeTime Supporter
Nov 18, 2009
835
Sacramento, CA
plucky71 said:
...Can I slowly use them to maintain my FC level and at the same time raise my CYA level? For example, add 1/4 or 1/8 of a bag, circulate, test FC and repeat the next day.
Absolutely! The TFP method doesn't preclude the use of pool store products, but rather promotes knowing what you are adding and why you are adding it.

Use the pool calculator "Effects of adding chemicals" section to estimate the amount of CYA that will be added and keep track so you don't overdo it.
 

Speedo

LifeTime Supporter
May 4, 2011
636
JasonLion said:
The normal approach is to raise CYA to 50 in the spring, so it will still be at least 30 in the fall.

Higher CYA levels require a higher FC level, but you actually need to add less total chlorine to maintain that higher level because the higher CYA level protects the chlorine from sunlight more effectively. The disadvantage is that higher CYA levels make it more difficult to fight algae, though this is not a big deal in the 30 to 50 range, it becomes important as CYA goes above 50.
This is exactly what I was looking for! I need to crunch my #s, but what I'm noticing (from memory) is that when my CYA was 90-95, 2 seasons ago I was burning up about 5ppm on a sunny day w/ swimmers. Targeting 11ppm and dosing up to around 16ppm at night. Last season my CYA was 65 and I set my target for 7, I recall losing around 3.5ppm on sunny days w/ swimmers. The past few sunny days with a CYA of what I estimated to be 45 (re-test I got 40) I was also losing 3.5ppm.

I start thinking about how the +/- 10 ppm accuracy could put me at 30. If my target was 4 and I dosed it up to 8, losing 3.5 would put me at 4.5. I don't want to assume that my CYA test was -10 from my result. After seeing this post I will add 10ppm CYA and target 6. Hopefully my average consumption is closer to 2.5-3.

Note: plenty of debris/leaves are falling in, I wouldn't be too surprised if that could account for some measurable loss.
 

tltmom

Platinum Supporter
LifeTime Supporter
Aug 5, 2011
196
Speedo-
not to barge in on this thread, but I'm in Central Illinois as well. Curious as to where your Cl started out and ended up with your CYA = 45. My CYA is the same and I'm still trying to figure out if the pool is loosing a bit too much Cl daily or not. Thanks.
 

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