chlorine balance

JBorderieux

New member
Jun 16, 2020
4
Forsyth, GA
I've had my pool for 1 year and just discovered this group. My water is clear and I've had very few problems. I have a 30,000 gallon gunite pool with pebble finish and ozone/uv system. I'm trying to wrap my head around the chlorine calculations I'm seeing. I usually run on the very low end (between 1 & 3). But, just playing with the calculator, it says because my CYA is 70 my target FC should be 6 - 10. Is that true? I've never had chlorine that high and always had clear water. Is it even safe to swim with FC that high?
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Welcome to TFP! :wave: Here we follow the FC/CYA Chart which was developed over years of study based on appropriate sanitary requirements for residential pool water across various salt and non-salt pools. If yours is a salt pool, we recommend a minimum CYA of 70 because chlorine gas is generated intermittently through the 24-hour cycle and the relatively low FC amount produced requires that CYA protection. For non-salt pools in extremely hot areas like here in TX, CA, AZ, NV, etc, a CYA of 50-70 is not unheard of as well. When following the FC/CYA Chart, the water is safe as long as the owner does not exceed the FC "SLAM" level for their current CYA. You can see more about these concepts at our ABCs of Pool Water Chemistry page. Hope that helps.
 
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IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,177
Milwaukee, WI
At CYA 70, it's safe to swim at levels up to 28ppm of FC.

That said - I don't know how you got the CYA 70 reading. If it's not from a test kit like the TFT-100 or the Taylor K-2006C, I don't know that I'd trust that number to be accurate. It could be much lower, which would mean 28ppm of FC would not be safe to swim in.

Knowing what your levels are by doing your own test with a reliable test kit is a cornerstone of what we do here. :)
 

JBorderieux

New member
Jun 16, 2020
4
Forsyth, GA
At CYA 70, it's safe to swim at levels up to 28ppm of FC.

That said - I don't know how you got the CYA 70 reading. If it's not from a test kit like the TFT-100 or the Taylor K-2006C, I don't know that I'd trust that number to be accurate. It could be much lower, which would mean 28ppm of FC would not be safe to swim in.

Knowing what your levels are by doing your own test with a reliable test kit is a cornerstone of what we do here. :)
I had it tested at 2 different pool stores - one said 70, the 2nd said 72. This new philosophy is totally different to me - I'm surprised my pool hasn't turned green in the last year. Do all these calculations/ratios stay the same even with Ozone/UV system in place as well?
 

JBorderieux

New member
Jun 16, 2020
4
Forsyth, GA
I had it tested at 2 different pool stores - one said 70, the 2nd said 72. This new philosophy is totally different to me - I'm surprised my pool hasn't turned green in the last year. Do all these calculations/ratios stay the same even with Ozone/UV system in place as well?
oh, and I ordered the K2006 yesterday. It should be here this week. I'm not making any major changes until I receive it.
 
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IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,177
Milwaukee, WI
I had it tested at 2 different pool stores - one said 70, the 2nd said 72. This new philosophy is totally different to me - I'm surprised my pool hasn't turned green in the last year. Do all these calculations/ratios stay the same even with Ozone/UV system in place as well?
Ozone only sanitizes the water that's in the chamber. Same with UV. If anything UV systems burn off the chlorine in the water going through them. Sadly we don't put much stock in those sorts of systems - a saltwater generator, on the other hand, keeps chlorine residuals in the pool.

Pool store testing is notoriously unreliable. They might be accurate but they might not - and we can't know which ones to trust. So we only trust test results taken by people and not by stores. :(

It's possible the Ozone/UV systems have kept your pool in check. Or that you have more chlorine or less CYA than you suspect. Or that you've just been lucky. But as bad as algae is, it's worse if someone gets a bacterial infection from the pool water - so it is really important to keep it properly sanitized.

oh, and I ordered the K2006 yesterday. It should be here this week. I'm not making any major changes until I receive it.
Good plan. How do you currently chlorinate?

Oh, and if it's the K-2006 and not the K-2006C, then you'll probably be running out of FAS-DPD powder and CYA reagent pretty quickly. You might want to get some refills on those now too. See Test Kits Compared for the number of each test you get. (The other ones are done so infrequently that you probably have enough in the K-2006...I don't think I'll ever use all of the TA, pH, or CH stuff that came with my K-2006C.)
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,501
NW Ohio
Welcome to TFP!

Do all these calculations/ratios stay the same even with Ozone/UV system in place as well?
UV and Ozone have no effect on the required chemical levels. Honestly, in an outdoor residential pool those units don't offer any tangible benefit. The UV from sunlight breaks down chlorine byproducts faster than the UV unit ever could and with the low bather load compared to a public pool the supplemental oxidation provided by ozone or sanitation provided by UV are wasted. In fact, running these can actually increase chlorine loss.
 

JBorderieux

New member
Jun 16, 2020
4
Forsyth, GA
Ozone only sanitizes the water that's in the chamber. Same with UV. If anything UV systems burn off the chlorine in the water going through them. Sadly we don't put much stock in those sorts of systems - a saltwater generator, on the other hand, keeps chlorine residuals in the pool.

Pool store testing is notoriously unreliable. They might be accurate but they might not - and we can't know which ones to trust. So we only trust test results taken by people and not by stores. :(

It's possible the Ozone/UV systems have kept your pool in check. Or that you have more chlorine or less CYA than you suspect. Or that you've just been lucky. But as bad as algae is, it's worse if someone gets a bacterial infection from the pool water - so it is really important to keep it properly sanitized.


Good plan. How do you currently chlorinate?

Oh, and if it's the K-2006 and not the K-2006C, then you'll probably be running out of FAS-DPD powder and CYA reagent pretty quickly. You might want to get some refills on those now too. See Test Kits Compared for the number of each test you get. (The other ones are done so infrequently that you probably have enough in the K-2006...I don't think I'll ever use all of the TA, pH, or CH stuff that came with my K-2006C.)
I've switched back and forth between tablets and liquid. Now that CYA is back to a higher range I am going back to liquid. I have a local pool store that makes and sells 10.5% by the 2.5 gallon jug for $5 each - seems reasonable but I haven't shopped it much.