Clarification on CYA and FC

[sjoshi]

I know the TFP recommendation for CYA is 70 - 80 (ish) for a SWCG pool. I also read somewhere that FC needs to be 7.5% of CYA for it to matter (according to one study). What do experts think about this 7.5%? Is it needed in practice?

The same article said that if you have CYA in the pool, then a higher pH will not necessarily reduce the effectiveness of the free chlorine. So say pH rises while you are away, you come back and fix pH - no increased risk of algae in the meantime with FC of 4 - 6 and CYA of 60 (roughly thats what i currently have)?

 

[Jimrahbe]

S,

7.5% is on the low end...

The whole point of the TFP pool care process is maintaining your FC and CYA in the proper relationship.

The reason that most people come to TFP with green and cloudy pools is simple because they are not keeping their CYA and FC at the proper levels.

What is your real question? What is it that you want to do??

Thanks,

Jim R.

 

[sjoshi]

S,

7.5% is on the low end...

The whole point of the TFP pool care process is maintaining your FC and CYA in the proper relationship.

The reason that most people come to TFP with green and cloudy pools is simple because they are not keeping their CYA and FC at the proper levels.

What is your real question? What is it that you want to do??

Thanks,

Jim R.

thank you. Was just curious if the 7.5% was reasonable, sounds like it is not. Needs to be higher.

Any thoughts on the pH part of the question?

What i am after ofcourse, is the lowest level of safe FC I can use and managing risk of pH rising in my SWCG pool if I am away for a week to 10 days. As to the pH question -- If the pH rises to say 8.3 but CYA is protecting FC effectiveness -- then i can just fix the pH when I am back before anybody goes into the pool.

 

[Newdude]

What i am after ofcourse, is the lowest level of safe FC I can use and managing risk of pH rising in my SWCG pool if I am away for a week to 10 days

Forget trying to eek the lowest. Please. Pretty PRETY PLEASE forget it. Obsess over having enough chlorine. Use even more than that and run 'hot' as we call it and you'll be covered for whatever the universe throws at your pool. Even 10 day trips.

Swimming is safe up to SLAM FC. And thanks to the CYA buffering it, it's less harsh than municipal water with no CYA and a FC up to 4.

As to the pH question -- If the pH rises to say 8.3 but CYA is protecting FC effectiveness -- then i can just fix the pH when I am back before anybody goes into the pool.

High PH may cause some eye irritation. It'll still probably be less than what you get in anyone else's improperly sanitized pool.

 

[Mdragger88]

.... "Min FC" is 7.5% of the CYA level
.... "Target FC" is 11.5% of the CYA level
.... "Yel/Mstrd Min" is 15% of the CYA level
.... "Shock FC" is 40% of the CYA level
.... "Yel/MstrdShock" is 60% of the CYA level.
From here & the basis for FC/CYA Levels

Chlorine/CYA Chart

EDIT: You will find a simplified and standardized version of this chart at Pool School, Chlorine / CYA Chart. Chlorine/CYA Chart by Chemgeek FC = Free Chlorine in parts-per-million (ppm) CYA = Cyanuric Acid in parts-per-million (ppm) CYA ........... Min FC3 ..... Target FC ...... Yel/Mstrd...

www.troublefreepool.com

As mentioned- minimum is just that - MINIMUM
you want TARGET range, flirting with minimum risks algae & nasties.
Fc Anywhere between minimum & slam level for your cya is safe for swimmers, equipment & surfaces so why risk it by riding the line?

 

[Jimrahbe]

S,

The amount of FC generated does not really have much to do with pH.

pH going a little high for a few days will not cause any major issues.

One of the great things about having a SWCG is being able to leave the pool to go on a vacation or trip.

In my mind, the minimum FC level does not even exist. My "minimum" is the low end of the target FC range. I always try to keep my FC in the target area or above. I never try to test out how low can I go...

Thanks,

Jim R.

 

[Oly]

Some car owners will fill up their fuel tanks or electric batteries whenever the gauge reads 1/2 or maybe 1/3 full.
Some wait until their low fuel light has been on for several days, then only put in $20 worth of fuel.
After a year both have spent the same on fuel if they have driven the same distance, same car, same style driving, pay the same price, etc.
It's not significantly more expensive or unhealty for a pool owner to stay well into the target range all day every day especially peak season.
In fact with the life's little distractions, emergencies and wild all day/night pool parties, the resulting unsanitized water and required SLAM will cost more heartache, time and $$ every time.

 

[sjoshi]

Ty all!

 

[Saturn94]

In my mind, the minimum FC level does not even exist. My "minimum" is the low end of the target FC range. I always try to keep my FC in the target area or above. I never try to test out how low can I go...

YES!!! THIS!!!