CYA and bleach protection revisited?

[Rangeball]

Richard, I recall reading a thread at poolsolutions last year where you showed a chart illustrating the majority of chlorine protection is obtained at 20 ppm, with minimal additional protection as CYA rises. Since then I've maintained my CYA at about 25, and keep my FC in the corresponding range per the best guess chart. My pool uses about 2 ppm of chlorine daily, get's probably 75% full sun daily, and is not covered.

I was reading some at pool solutions in the PH rising thread there, and Richard said he was rethinking using a minimum CYA level. I'd like to hear what your current thoughts are, and if possible, I'd be interested in increasing my CYA if it will allow me to reduce my bleach consumption. I manually add at night.

One thing I do like about my current approach is the ability to use the OTO test without dillution. I assume a higher CYA still means a higher FC?

 

[chem geek]

See the later posts in this thread for the latest in the discussion on this topic as well as this post for some technical details.

You are correct that you would still need to use a higher FC level at the higher CYA level. There is nothing in that aspect of the chemistry that is changing. The main change to the CYA protection of chlorine theory is that the protection does not only come from having less unbound chlorine that is susceptible to sunlight (and a bound chlorine to CYA that is less susceptible), but that additional protection comes from a shielding (absorption) effect from CYA itself. It appears that this shielding effect is so strong that it makes it worth it to have higher CYA with correspondingly higher FC. That is, the shielding effect saves more chlorine than is lost by having to have a higher FC due to the higher CYA.

In theory, this shielding effect should be even greater in deeper pools, but experiments Mark has done show the effect to be quite strong so even a spa is significantly affected and even a bucket of water seems to be shielded quite a bit. We haven't done experiments in shallow pans yet, but I would say that if you are losing a lot of chlorine per day due to breakdown from sunlight (so your chlorine is holding at night), then increasing both CYA and FC may help reduce total chlorine consumption.

Of course, the difficulty is that it is not easy to "go back" to lower CYA if you don't find an improvement. Also, you are right that you can't use the simple quick OTO test to know if you have enough chlorine since it only measures roughly to 5 ppm FC (without dilution). You'll know you have some FC, just not if it's enough. The target FC needs to be around 11.5% of the CYA level (an absolute minimum of 7.5% of the CYA level -- that corresponds to Ben's "Min" column).

Richard

 

[Rangeball]

Of course, the difficulty is that it is not easy to "go back" to lower CYA if you don't find an improvement. Also, you are right that you can't use the simple quick OTO test to know if you have enough chlorine since it only measures roughly to 5 ppm FC (without dilution). You'll know you have some FC, just not if it's enough. The target FC needs to be around 11.5% of the CYA level (an absolute minimum of 7.5% of the CYA level -- that corresponds to Ben's "Min" column).

Richard

Richard, thanks for your thoughts.

With a CYA of 25, per your percentage calculations my target FC is 2.9 and minimum is 1.9. I've been trying to maintain between 3 and 5. No wonder I'm losing 2 ppm daily. It's not being protected. Makes sense now

I guess I should let it drop to 3, then monitor it overnight, then the next evening to see what my actual loss for CYA protected FC is. I may be able to go 2 days between adding bleach, effectively cutting my bleach bill in half.

Thanks again. I'll update this when I've done my testing.

I've never tested to see what I'm holding overnight as I haven't had any problems. Best bet is to test after sundown, then again prior to sun-up and compare the two?

 

[chem geek]

Yes, measuring after the sun goes down and soon after the sun come up is fine. The sun at a low angle is very, very weak so doesn't break down much chlorine.

Your rate of chlorine loss from breakdown by sunlight at 3 ppm FC should be about half that at 6 ppm FC so you should see less chlorine usage IF all of the usage is from breakdown from sunlight. I suspect that at least some of it is from breakdown of organics -- perhaps up to 0.5 ppm FC per day if you have a lot of junk in your pool or use it regularly. The overnight loss will give you an idea of this "other" non-sunlight usage.

Be careful about trying to just skate above 2 ppm FC. With some extra chlorine demand, you could go below and your water may start to cloud up from a nascent algae bloom. That happens in my pool if I'm lax and get too low -- I've got around 30 ppm CYA so not far from yours. The cloudiness occurs if I get below 2 (the "Min" is 2.25 so it's really a "hard" minimum).

Richard

 

[Shelley N]

This is exciting understanding this thread and knowing what it means to me.

My CYA is somewhere between 20 and 30. I've been keeping my CL at around 6 as insurance that I don't go below my minimum at any given time as I never ever want to see even the slightest hint of a problem in my water. So my insurance is costing me in the CL that is unprotected by the CYA. In my situation that probably equates to about 1 quart of CL a day, somewhere around $.52 worth.

I've been adding CL nightly because of the high temps (99), the fact that my pool is in the full sun from 7am to 6pm, and the high # of kiddos in my pool (at least 6) daily. I would love to go to an every-other-day addition of CL at night, but can it be done? You add CL over the protection value of the CYA and it just burns off...right? How do you add enough to get you through a couple days and not have the CL too high to swim in (drink per the younger kids)?

Shelley

 

[Rangeball]

This is exciting understanding this thread and knowing what it means to me.

My CYA is somewhere between 20 and 30. I've been keeping my CL at around 6 as insurance that I don't go below my minimum at any given time as I never ever want to see even the slightest hint of a problem in my water. So my insurance is costing me in the CL that is unprotected by the CYA. In my situation that probably equates to about 1 quart of CL a day, somewhere around $.52 worth.

I've been adding CL nightly because of the high temps (99), the fact that my pool is in the full sun from 7am to 6pm, and the high # of kiddos in my pool (at least 6) daily. I would love to go to an every-other-day addition of CL at night, but can it be done? You add CL over the protection value of the CYA and it just burns off...right? How do you add enough to get you through a couple days and not have the CL too high to swim in (drink per the younger kids)?

Shelley

Shelly, as I understand Richard, and let's assume your CYA is 25, the average of "somewhere between 20 and 30"-

Target FC is 11.5% of CYA, for a CYA of 25 ppm = 2.9 ppm, which we'll round to 3 ppm.
Minimum FC is 7.5% of CYA, for a CYA of 25 ppm = 1.9 ppm, which we'll round to 2 ppm.

Yes, anything you add above the 3 ppm is unprotected and will be burned off quickly in direct sunlight. However, like you stated, if it's added at night it's available for sanitizing "insurance".

If you let your FC drift down to 3, tested after the sun goes down, and it's still holding at 3 the next morning before the sun comes up, you don't have any organics using it up. If it only goes down slightly by the next evening, you can probably continue testing and only add once it hits the minimum of 2, taking it back up to 3 again, then repeat.

At the cost you cited for your bleach needs, there's not much to be saved. Like you even if I change what I'm doing it will only make a difference of $15 per month in bleach cost, and like you said, it's cheap insurance to stay away from problems. Staying ahead of your pool is paramount, and like you I don't really want to jeapordize this and have to spend all the savings correcting problems. We may be able to only add bleach every other day with this method, but we'd have to pay more attention to our levels as we don't have much wiggle room with 1 ppm between target and minimum.

 

[chem geek]

The interesting possibility, however, is that if you increase your CYA a lot -- to 60-80 ppm -- and increase your FC level accordingly to a target of 6.9 - 9.2 ppm FC (an absolute minimum of 4.5 - 6.0), then it is possible that you will lose less chlorine per day even though you have a higher FC level. Though the higher FC level increases the rate of loss at the same CYA level, the higher CYA level protects the chlorine at an even greater rate (through additional shielding of CYA by itself by absorbing the sun's UV above and beyond just combining with chlorine). This is what we are figuring out. Several users are able to add chlorine less frequently by having higher CYA levels, even with higher FC levels to maintain disinfection and to prevent algae.

If it were easy to lower the CYA level, I'd just say you should try the higher CYA (with higher FC) to see if it helps in your situation. Unfortunately since only dilution reduces CYA this isn't an easy experiment to try (in a large pool -- it's easy in a spa).

Richard

 

[Rangeball]

Richard, how far away do you think you are from being able to generate a new improved CYA protection chart?

If it were conclusively proven, I'd do that in a heartbeat.

As for testing in a pool, is it possible to take someone with an SWG that already has the elevated CYA levels, have then turn off the SWG then run the tests with bleach as you propose to get the data?

When the test is over they could simply go back to the SWG. Seems easy, but I'm sure I'm missing something

 

[chem geek]

Mark (mas985) is already doing tests using both his pool and his spa (which he can easily adjust in CYA level). I'm about 90% confident, based on his tests, that the higher CYA levels protection is faster than a linear or proportional rate, at least going from 45 ppm CYA to 80 ppm CYA as Mark was doing. Putting together a full graph is going to take a lot more data though I'll probably do a rough one based on his results and the theory of CYA absorption.

I wish I could be more definitive for you. At this point, it's likely that increasing your CYA level will help reduce chlorine usage. But I can't tell if there's a bow in the curve so that at very low CYA the loss is similar to high CYA (i.e. the curve could be umbrella shaped). Because the CYA absorption protection is non-linear, low CYA behaves the way we used to think ("less is better") while higher CYA behaves in a "more is better" manner. I just don't know where the transition point is, except that it's roughly below the 45 ppm CYA low-end that Mark is testing.

At high CYA and high FC, the disinfecting chlorine level will be the same (assuming one sets the FC level appropriately) so oxidiation and prevention of algae will be the same. The higher overall FC does mean a higher capacity or quantity of chlorine in a given volume of water. So the water is clearly safe to swim in, but as for younger kids that may drink pool water they will get more chlorine in their systems at the higher FC. Unless they drink an awful lot and do so regularly, it's still far below having problems, but it IS more chlorine (around 3 times more if one goes from 25 ppm CYA to 75 ppm CYA with a corresponding increase in FC). I think the bigger concern would be for the dogs that drank 1-2 quarts per day from the pool (though Borates were more of an issue that chlorine in that case, but with higher chlorine levels it gets closer to the "just noticeable" problems with Borates).

Richard

 

[Rangeball]

Interesting.

I think for the relatively small savings (assuming a 50% reduction in bleach) potential, I'll wait this one out.

Thanks for your input

 

[itabb]

What's the problem with Dogs and Borates? And do I need to worry about my 1 year old drinking a lot of pool water while learning to swim with a FC 6 and CYA 80 and Borates 30ppm (SWG)?

 

[chem geek]

The risk for the Borates is low, but is about at the level of first detectable symptoms in dogs if they drink a lot -- over a pint per day at 50 ppm so closer to a quart a day at 30 ppm. Details may be found here. One study found decreased spleen-to-body-weight ratio at 0.44 mg/kg in males while another study found no effects until 29 mg/kg (8.8 mg/kg showed no effects). So taking 0.44 mg/kg, for a 20-pound (9 kg) dog, then that's 4 mg which at 50 ppm (mg/liter) is 80 ml or 2.7 fluid ounces. If we use the 8.8 mg/kg number, then we get 79 mg which at 50 ppm is 1.6 liters or 1.7 quarts.

If you read the text and try and sort it all out, it sounds like the 0.44 study phenomenon was a fluke and the 8.8 number is probably closer to reality. In any event, it's probably a good idea to teach your dog to drink from a water bowl instead of the pool.

For comparison, this link gives details on chlorine. Up to 100 ppm chlorine given to rats every day in their drinking water did not result in problems. At 26 ppm, the inhalation route caused serious problems in rats. My guess is that saliva inactivates much of the chlorine before it becomes a problem (or its inactivated in the stomach before being absorbed elsewhere).

 

[Rangeball]

Mother nature forced my hand last night

I had tested the pool at about 6 pm, around the time the pool is out of direct sunlight. I had planned to add bleach last night per my usual routine, but it was raining. Hard.
So I skipped it.

Tested the pool this morning with OTO. Seemed to me the chlorine held to the same level as the night before, but OTO is so subjective in different light levels.

 

[Rangerman]

I have a CYA level of 40 and I'm adding about 180 oz of 6% bleach every other day. Is this about right for 30,000 gals. in full sun everyday?
Hope everyone's summer is going nicely !!

 

[JasonLion]

I have a CYA level of 40 and I'm adding about 180 oz of 6% bleach every other day. Is this about right for 30,000 gals. in full sun everyday?

How much chlorine you lose depends on your CYA level, the average depth of the pool, how much sunlight you get, what FC level you start with in the morning, how much organic debris falls into your pool, the water temperature, bather load, and other factors.

180 oz of 6% in 30,000 gallons is about 3 ppm of FC. Given plausible default values for each of those factors, losing 3 ppm of chlorine each day sounds reasonable.

 

[Guest]

Mark (mas985) is already doing tests using both his pool and his spa (which he can easily adjust in CYA level). I'm about 90% confident, based on his tests, that the higher CYA levels protection is faster than a linear or proportional rate, at least going from 45 ppm CYA to 80 ppm CYA as Mark was doing. Putting together a full graph is going to take a lot more data though I'll probably do a rough one based on his results and the theory of CYA absorption.

Richard

Drawing conclusions from one pool is rather risky, is it not? I would feel better if data could be collected from a number of pools This is really uncharted waters (unlike the experiment I did on Poolfourm with borates where I was trying to see if they actually lived up to the various claims made about them.) I think it is a bit early to jump to conclusions about CYA effects/chlorine chlorine retention based on data collected from one pool/spa. I think caution is to be advised here!

 

[Rangerman]

I have a CYA level of 40 and I'm adding about 180 oz of 6% bleach every other day. Is this about right for 30,000 gals. in full sun everyday?

How much chlorine you lose depends on your CYA level, the average depth of the pool, how much sunlight you get, what FC level you start with in the morning, how much organic debris falls into your pool, the water temperature, bather load, and other factors.

180 oz of 6% in 30,000 gallons is about 3 ppm of FC. Given plausible default values for each of those factors, losing 3 ppm of chlorine each day sounds reasonable.

Thanks - good to know I'm on track. BTW - the pool looks spectacular this year using the BBB method.

 

[chem geek]

Drawing conclusions from one pool is rather risky, is it not? I would feel better if data could be collected from a number of pools This is really uncharted waters (unlike the experiment I did on Poolfourm with borates where I was trying to see if they actually lived up to the various claims made about them.) I think it is a bit early to jump to conclusions about CYA effects/chlorine chlorine retention based on data collected from one pool/spa. I think caution is to be advised here!

Yes, you are right -- I'm really only thinking that the SWG efficiency isn't improved, at least for his SWG system, going from 45 to 80 ppm CYA. He repeated that and got consistent results, but it's possible that different SWG systems are different.

He also found noticeable increases in FC protection at the higher CYA level beyond that predicted from the CYA level alone. It's possible to have different amounts of sun on the different days or other factors in the spa since chlorine consumption can come from several sources (sun, organics, algae, etc.). But at least two (maybe three) other users in their own pools noticed substantial improvement in chlorine retention at higher CYA levels, even without an SWG system. If it had just been Mark's experiment, I wouldn't be as confident, but when several users report substantial savings well beyond what the chlorine/CYA relationship predicts AND when I find scientific documents showing CYA absorption of UV light (though declining rapidly in the region that overlaps hypochlorite ion absorption), I think that's strong evidence. Not full proof, but multiple sources of evidence.

What Mark found is not inconsistent with what happened in your pool. An increase in CYA let you cut down the SWG time. It is not necessary that this come from higher SWG efficiency -- a non-linear CYA protection (i.e. an absorption/extinction effect) would also account for it. The Borates effect seems less consistent among pools (it worked well for your pool and not in some others) so that's possibly more dependent on the amount of nascent algae that the Borates can kill instead of chlorine getting used up doing the same thing.

We'll see how this all pans out with more data.

Richard

 

[Guest]

Another factor with SWGs that has been overlooked is the size of the cell relative to the size of the pool. My cell is able to produce enough clorine to keep my FC levels up even with NO CYA and the large amount of sunlight my pool gets becaue it is rated for residentail pools up to 40K and commercial poos up to 25K and my poo is less than 7k. Most salt setups are not that oversized! Also, my filtration meets the requirements for a commercial pool (The one thing my PB did right!)

I have seen a lot of salt pools at work and most of them cannot operate without the recommened dose of CYA in the water. There are also a few salt generators that recommend CYA of 80-100 ppm. What if find interesting is that two of these are made in Arizona (I suspect by the same company) I don't kow if this is because the amount of sunlight pools are exposed to there or if it is because the cells are actually undersized. It would be interesting to fnd out. They are Pool Ex and the other is PoolThing. Every other manufacturer that I have seen puts an upper limit of 75 or 90 ppm (which are essestially the same thing, given that the accuracy of CYA testing is +/- 10 ppm at best and in actual practice is really much larger!. In fact, LaMotte's testing with a colorimeter and they chemistry is+10/-25 ppm so this throws another problem into exactly at what level do the effects of CYA and chlorine protection actually cut in.

 

[JasonLion]

Several people have reported that CYA around 80-90 reduces bleach usage compared to CYA around 30-50. I take Mark's experiments as confirmation of this anecdotal evidence. And if you discount the CYA improves SWG efficency theory the high CYA recommendations of SWG manufacturers supports this as well. The only evidence to the contrary appears to consist of a single study whose methods are not totally applicable (they appear to have used relatively shallow containers of water).

My view is that we are well beyond the single experiment awaiting confirmation stage and have moved along to high CYA reduces chlorine consumption as the default, though not yet 100% sure, view.