The rate of chlorine decay

[hexabc]

I have 30 ppm of CYA in my pool. Today on a beautiful sunny day I conducted a little experiment. Measured FC at 11am (5ppm) and then at 2:30pm (3.5ppm). The rate of chlorine loss = 1.5 / 3.5 = 0.43 ppm/hour. I’m wondering : would my pool benefit from increasing CYA to 40 ?

 

[jblizzle]

Higher CYA will certainly better protect the FC from the sun.

The loss you measured was at peak sun, so obviously the loss would be less earlier and later.

 

[Wulfdan]

Yes. 40CYA will reduce your daytime losses

 

[Spa Owner]

UV destruction of chlorine can be huge. I have a property painted white, facing the sun with a pool in front of it. In summer with a clear blue sky, the pool can measure 15 ppm at 7.00am and 0 by 10.00am with 30 ppm of CA. Our UV is a bit more intense, but still this is something to see.

 

[duraleigh]

In summer with a clear blue sky, the pool can measure 15 ppm at 7.00am and 0 by 10.00am with 30 ppm of CA.

Then something is wrong. A pool with 30ppm CYA should experience a loss of maybe 4 ppm daily.....not 15 in 3 hours.

Why are you chlorinating to 15 ppm to begin with?

Where in the world is Victoria Park?

 

[Spa Owner]

Then something is wrong. A pool with 30ppm CYA should experience a loss of maybe 4 ppm daily.....not 15 in 3 hours.

Why are you chlorinating to 15 ppm to begin with?

Where in the world is Victoria Park?

Vic Park is in Western Australia.

15 mg/l is required to enable us to pass department of health microbial testing anything less wont get rid of all the bugs. Bit of a story, used to be 10 mg/l was good always, then we started running out of water, they started mixing water sources and then 15 mg/l is the minimum I need to be certain of no bugs on first test. Now I am up to 20 mg/l for 24 hours as the bugs have got smarter or something.

As a general rule for CYA here in this state in this part of the world, 50 mg/l is the minimum needed to have any discernible effect on chlorine consumption and further north they commonly run 70 mg/l or more.

Very different here to other parts of Australia let alone other parts of the world.

 

[duraleigh]

As a general rule for CYA here in this state in this part of the world, 50 mg/l is the minimum needed to have any discernible effect on chlorine consumption and further north they commonly run 70 mg/l or more.

Higher temperatures affect chlorine loss but your climate seems temp-wise like New Jersey or maybe upstate NY....certainly nothing extreme. A CYA of 30 ppm should have a discernible affect on your FC loss and certainly prevent FC from going from 15 ppm to zero in four hours.....I can't make that make sense.

Your local climate has some affect on your FC but CYA that you use is the same CYA that we use.

 

[Poolzzz]

7am -10am is only 3 hours. Since they are morning hours where UV is maybe 1/3 of the peak noon level I vote for something else happening if you are losing 15 to 0 in that time frame. Perth isn't that much different in UV than LA.

Also cya=50 as the minimum level to see any discernable effect doesn't sound quite right. Half life of chlorine is about 35 minutes at cya=0 and jumps to about 5 hours with cya=30. In other words 80% of the effect has happened by cya=30. So the big improvements occur well before cya=50.

 

[Spa Owner]

7am -10am is only 3 hours. Since they are morning hours where UV is maybe 1/3 of the peak noon level I vote for something else happening if you are losing 15 to 0 in that time frame. Perth isn't that much different in UV than LA.

Also cya=50 as the minimum level to see any discernable effect doesn't sound quite right. Half life of chlorine is about 35 minutes at cya=0 and jumps to about 5 hours with cya=30. In other words 80% of the effect has happened by cya=30. So the big improvements occur well before cya=50.

Perhaps there...Here CYA 30 will loose chlorine so fast we need a tanker to get the chlorine in fast enough. Its not me, others have tried on this site and someone thought it a smart idea, despite our advice to fit a BECS controller that cant handle CYA above 20 they lasted 3 months before the contractor was forced to replace at their cost with a better controller.

Sorry, this is a peculiar situation to us. I think its UV intensity here is way higher than other parts of the world due to ozone depletion being closer to us.

 

[Flying Tivo]

The Semi Commercial Application might have something to do with your FC loss. Doesn't make sense to me either!

Felipe

 

[Poolzzz]

Sorry, this is a peculiar situation to us. I think its UV intensity here is way higher than other parts of the world due to ozone depletion being closer to us.

I know you think it's UV...that's what you said in your first post. But you ignored all my points and just repeated your belief.

I'm saying from 7am-10am the UV levels in Perth isn't anything special. And certainly not high enough to lose in 3 morning hours way more than someone in LA would experience all day.

Feel free to post up the UV levels in Perth from 7am-10am. Pretty sure you're going to find it's not enough to explain the loss.