Chlorine / CYA Chart-- why

[Notri4MeBikeSwim]

from pool school
Chlorine / CYA Chart

Perhaps a cornerstone element of BBB is understanding the relationship between the chlorine in your pool and the stabilizer you put in to protect the chlorine from the sun. Generally, the more stabilizer, the more chlorine you need to maintain its effectiveness.


QUESTIONS;

1. if chlorine "conditioner/stablizer" drops evaporation of chlorine, why is more needed at higher cya levels?

2. Raised cya from 30 to 50. I was trying for 40 but put in too much conditioner. I expected to see less need
for FC additions of chlorine bleach, but that hasn't changed. Why not?

3. What does conditioner salt do? Obviously it changes the chlorine bleach into something. Doesn't this chemical change use up the conditioner over time, or is it a true catalyst

 

[PridgNYC]

from pool school
Chlorine / CYA Chart

Perhaps a cornerstone element of BBB is understanding the relationship between the chlorine in your pool and the stabilizer you put in to protect the chlorine from the sun. Generally, the more stabilizer, the more chlorine you need to maintain its effectiveness.


QUESTIONS;

1. if chlorine "conditioner/stablizer" drops evaporation of chlorine, why is more needed at higher cya levels?

2. Raised cya from 30 to 50. I was trying for 40 but put in too much conditioner. I expected to see less need
for FC additions of chlorine bleach, but that hasn't changed. Why not?

3. What does conditioner salt do? Obviously it changes the chlorine bleach into something. Doesn't this chemical change use up the conditioner over time, or is it a true catalyst

1. CYA or conditioner, doesn't 'prevent evaporation' as you are thinking of it. It binds to free chlorine and prevents degradation by UV light, but at the same time it also prevents it from interacting with other organic molecules. That is why you need more FC for a given level of CYA.

2. With less CYA, you lose more FC to sunlight degradation so you have to add a certain amount periodically to keep up with the loss. The important point is that it is time based, less cya means that your half-life (the amount of time it takes for half of your FC to disappear) is lower, so you have to add bleach more often. Higer CYA levels will extend the time between you having to add bleach but doesn't necessarily change the amount of bleach that needs to be added to maintain effective FC levels for your level of CYA.

3. Conditioner Salt? I assume you mean the salt added to a pool in order to run a salt water generation system. Without an SWG (Salt Water Generator), it has no effect on chlorine usage or anything else except your TDS test. If you have a Salt Water Generator, then it will convert the salt in the water to chlorine so you don't have to keep adding bleach all the time. The chlorine that the SWG creates from the salt is the same chlorine you get from bleach, but it is basically recycling the chlorine in the salt every day so your need to add bleach is minimal.

 

[chem geek]

a given level of CYA.
Higer CYA levels will extend the time between you having to add bleach but doesn't necessarily change the amount of bleach that needs to be added to maintain effective FC levels for your level of CYA.

There is a non-linear effect of CYA protecting chlorine from the UV in sunlight so even when the FC is proportionally raised when the CYA level is higher, the absolute FC loss is lower so less bleach needs to be added over time. The table in this post gives a rough idea of the effect, though for any given pool there are a variety of factors that determine the actual chlorine loss including amount of sunlight, temperature, bather load, circulation and other factors. Usually though, sunlight is the greatest source of chlorine loss in residential pools since they are typically low bather-load.

 

[Notri4MeBikeSwim]

Thank you. I called the conditioner salt as this was part of the description on the bottle of "conditioner" and the bottom of the bottle looked more like salt going into the pool than a typical liquid.

So if I understand correctly, there is no real value in raising cya from 30 to 50 and during the fall I should start loosing water to lower the cya back to the 30 range.

 

[jblizzle]

If you have a lot of sun, then there is certainly value in raising the CYA level because you will lose less too the sun. While the FC level may be higher, you should be able to add less each day.

 

[kmdigital]

from pool school
Chlorine / CYA Chart

Perhaps a cornerstone element of BBB is understanding the relationship between the chlorine in your pool and the stabilizer you put in to protect the chlorine from the sun. Generally, the more stabilizer, the more chlorine you need to maintain its effectiveness.


QUESTIONS;

1. if chlorine "conditioner/stablizer" drops evaporation of chlorine, why is more needed at higher cya levels?

2. Raised cya from 30 to 50. I was trying for 40 but put in too much conditioner. I expected to see less need
for FC additions of chlorine bleach, but that hasn't changed. Why not?

3. What does conditioner salt do? Obviously it changes the chlorine bleach into something. Doesn't this chemical change use up the conditioner over time, or is it a true catalyst

1. CYA or conditioner, doesn't 'prevent evaporation' as you are thinking of it. It binds to free chlorine and prevents degradation by UV light, but at the same time it also prevents it from interacting with other organic molecules. That is why you need more FC for a given level of CYA.

2. With less CYA, you lose more FC to sunlight degradation so you have to add a certain amount periodically to keep up with the loss. The important point is that it is time based, less cya means that your half-life (the amount of time it takes for half of your FC to disappear) is lower, so you have to add bleach more often. Higer CYA levels will extend the time between you having to add bleach but doesn't necessarily change the amount of bleach that needs to be added to maintain effective FC levels for your level of CYA.

3. Conditioner Salt? I assume you mean the salt added to a pool in order to run a salt water generation system. Without an SWG (Salt Water Generator), it has no effect on chlorine usage or anything else except your TDS test. If you have a Salt Water Generator, then it will convert the salt in the water to chlorine so you don't have to keep adding bleach all the time. The chlorine that the SWG creates from the salt is the same chlorine you get from bleach, but it is basically recycling the chlorine in the salt every day so your need to add bleach is minimal.

So if you have a dark (no sunlight gets through), waterproof, motorized pool cover that's on 99% of the time, you should be able to keep the CYA at the very minimum levels, or maybe even as low as 10? Just wondering since it seems like there would be very little chlorine degradation due to sunlight, and having minimal CYA would very drastically reduce the requisite FC levels.

 

[JasonLion]

You don't actually want to lower FC level that much. You need enough chlorine in the pool to handle the "instant" demand from several people entering the water. At very low FC levels that will consume all of the available chlorine, leaving you with a problem. The more dangerous forms of CC are also more likely to be created at lower FC levels. Meanwhile, even with an opaque cover, you want some protection from sunlight or you will lose most of your chlorine each time the cover is open. With the opaque cover, I do recommend CYA down at the low end of the normal range, ie around 30. There are also secondary issues because none of the common CYA tests will measure CYA levels below about 20.

 

[kmdigital]

Okay, thanks. That's kind of what I figured and it makes sense, but thought I would ask.

 

[Irishterrier74]

Great thread! Real expert answers. You guys are pros.

 

[scott.MI]

So if you have a dark (no sunlight gets through), waterproof, motorized pool cover that's on 99% of the time, you should be able to keep the CYA at the very minimum levels, or maybe even as low as 10? Just wondering since it seems like there would be very little chlorine degradation due to sunlight, and having minimal CYA would very drastically reduce the requisite FC levels.

I thought the same as you when I asked a question about wanting a low CYA in a hot tub that's used rarely and always covered, and even under a gazebo. Here's another reason for not having that low of CYA that I got in response. They recommend about a 30CYA even for hot tubs with covers.

Remember that the purpose of the CYA isn't so much to protect chlorine from sunlight because there won't be any in most spas with tight covers and that are often used at night. The reason for the CYA is to moderate chlorine's strength. If there were no CYA in the water, then the chlorine would be too strong and would oxidize swimsuits, skin and hair faster so would be more irritating and it would outgas faster so it would get used up more quickly and oxidize hot tub covers faster and possibly smell more (usually by forming chloramines in your nose). It would also produce disinfection by-products faster and for nitrogen trichloride, in greater quantity.

 

[kmdigital]

Ahh, very good to know. So minimum is 30, no matter what, and it makes sense. Much appreciated.