CYA in a Bromine Pool

In this post Ben wrote the following:

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Stabilizer has little or no effect on bromine, so as long as some bromide (from past bromine use) remains in the pool, you will have an UNstabilized bromine pool . . . even though you are adding chlorine.

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While it is true that there is no evidence that bromine combines with CYA the way that chlorine does so does not get any direct sunlight protection through reduction in hypobromous acid levels, that does not mean that there is no protection from degradation from sunlight at all from CYA. CYA appears to protect chlorine through two different mechanisms -- not only from combining with chlorine, but also through a direct shielding effect where CYA absorbs UV from sunlight protecting lower depths of the water. It is this effect that probably explains what is seen when one gets to higher 80 ppm CYA levels where the rate of chlorine loss is lower even when the FC/CYA ratio is kept the same meaning that the amount of hypochlorous acid is the same.

So it is possible that this same CYA shielding effect would help protect bromine as well -- the main question is how much. Since CYA doesn't make the bromine ineffective, one could raise the CYA to 100 ppm and see if the amount of added chlorine needed to sustain a constant bromine level is reduced in a pool exposed to sunlight. Lower CYA levels such as 30 ppm would not be expected to have a noticeable effect.

Richard

Richard;

Very interesting. I've glanced at the spectral absorption data you sent or linked, and it's definitely stuff I want to digest later.

I think this might be something to test, if we work that out. (In fact -- an experimental design for such a test just occurred to me -- I'll email you b4 I forget it.) But for practical purposes, if CYA only provides significant shielding at 80ppm or higher, for forum response purposes, that's probably a complication we don't need to include in posts to general users.

I've been thinking a lot about our conversation the other evening -- thanks for your time -- and am realizing that we are going to need some formal K.I.S.S. rules. There's a balance between oversimplifying and burying someone with more info than they can handle. I don't know where the line is, but we'll need some rules. Both of us err on the side of too much . . . too often.

At the same time, how do you know when additional info becomes too much? I don't know the answer, and I'm sure any answer agreed on will necessarily be arbitrary at points. But, I am sure I want transparency to ALWAYS be part of what we do here. In this case, that would mean that we always make the more complex info accessible, and always acknowledge that there's more complexity than what we address in a given post to a given pool owner.

Ben

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Originally Posted by PoolDoc

At the same time, how do you know when additional info becomes too much?

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Run it by Lisa or me--we're pretty much non-technical folks, and if we can't stay with it long enough to read the whole post,(which happens sometimes when you two get interested in something), that's too much additional info!!

Janet

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Originally Posted by PoolDoc

But for practical purposes, if CYA only provides significant shielding at 80ppm or higher, for forum response purposes, that's probably a complication we don't need to include in posts to general users

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The higher CYA level seems to be best for SWCG pools since they tend to have a big problem with rising pH and by having the higher CYA levels they are able to lower chlorine demand and turn down the SWCG on-time and reduce the rate of pH rise. This, along with a lower TA, seems to control the SWCG pH rise problem reasonably. Adding 50 ppm Borates can help as well.

At 80 ppm CYA, SWCG pools seem to be able to do well even with 4 ppm FC rather than the 5-10 in the Best Guess CYA chart that seems better suited to manually dosed pools. However, I agree with you that for manually dosed pools the risk of missing a dose, getting low chlorine, and then having to shock to deal with algae becomes harder at the higher CYA levels. There are some people with manually dosed pools in very hot sunny areas that are running at higher CYA levels, but most don't. Then there's Pool Chlor who use 100 ppm CYA and add chlorine to 14 ppm FC each week where it drops to around 4 ppm by the next visit. So even in hot sunny areas like Arizona, the daily chlorine loss rate at that high CYA level is around 16% per day.

It's not that magically there is protection at 80 ppm, but the increased level of protection seems to be non-linear and somewhere between 60-80 ppm it climbs fairly rapidly. This is the sort of thing that can be determined from experiment. I got your E-mail and replied.

For a number of years the SWCG folks, both pros and owners, have been aware that the "Best Guess Table" overstates THEIR required chlorine levels for the higher CYA levels required.

Normal CYA levels for them of 70 or 80ppm with FC levels of roughly 2-4 seem to easily keep their pools sanitary because the FC level is far more constant than in a manual pool.

But Ben's point of laying out practical, simple, and understandable steps to recommend is the equally valuable flip side of taking pool maintenance from alchemy to chemistry (the struggle we are all engaged in).

After all, most of us users aren't going to understand or care about molecular interactions by which bleach, which is not pH neutral, creates a reaction by the release of chlorine in exactly the opposite direction that zeroes it out. We WILL understand the bleach doesn't alter pH.

We want and need to advance the art and science of pool care, but to be useful we need to turn this into both practical steps and a clear decisive decision tree to follow to get to the ultimate goal:

A safe, sanitary swimming pool that's easy to maintain and is available for swimmers as much as possible.

That's why the China Shop is a great place, actually THE place to discuss theory, new concepts and experiments.

That's why this thread is here in The China Shop.

I don't know whether the lower minimum FC/CYA levels for SWCG pools are due to the more consistent dosing or due to the superchlorination of some of the water passing through the cell. It's likely to be some combination of both. Obviously, the superchlorination doesn't do anything for algae stuck on pool surfaces and would only affect planktonic (free-floating) algae.

It would not be hard to have a separate recommendation/table for SWCG pools compared to manually dosed pools without having to go into detailed explanations for why. Since SWCG pools have the pH rise problem and since that is proportional to the SWCG on-time which is proportional to the daily chlorine demand which is proportional to the FC level assuming a constant CYA level, it is important to have the lowest effective FC level in order to minimize the rate of pH rise.

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Originally Posted by chem geek

It would not be hard to have a separate recommendation/table for SWCG pools compared to manually dosed pools without having to go into detailed explanations for why. Since SWCG pools have the pH rise problem and since that is proportional to the SWCG on-time which is proportional to the daily chlorine demand which is proportional to the FC level assuming a constant CYA level, it is important to have the lowest effective FC level in order to minimize the rate of pH rise.

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All we need is one and then we can sticky it! I think that would be a GREAT addition!:)

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Originally Posted by CarlD

All we need is one and then we can sticky it! I think that would be a GREAT addition!:)

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You mean like this?
http://www.poolforum.com/pf2/showpos...9&postcount=22

Nope. A table like the "Best Guess Table" only a "SWCG Best Guess Table".

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Originally Posted by CarlD

Nope. A table like the "Best Guess Table" only a "SWCG Best Guess Table".

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For an outdoor pool with a SWG:
CYA 80-100 ppm (use SWG manufacturer's max number)
FC 3-5 ppm
Shock, if and when needed to 20 ppm with bleach

These numbers work.

I would also add:
TA 60-80 ppm
pH 7.6 to 7.8
CH 350 to 400 ppm (for plaster and fiberglass)
borates 50 ppm

These parameters will give the best pH stability, which will vary with each pool because of such variations as water features, assuming cured plaster.

No need for a chart since keeping the CYA at 80 or 100 ppm is important for pH stability since it translates into less cell on time.
One set of parameters is all you need based on the CYA of 80 or 100.

That's a really, really small table, 'Bear!:rolleyes:

Reminds me of the world's shortest poem called:

"Fleas"

Adam
Had'em.

:eek:

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Originally Posted by CarlD

That's a really, really small table, 'Bear!:rolleyes:

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Well, It's all you need!;)

I remember there was at least one SWCG pool owner who tried to use 3 ppm FC with 80 ppm CYA, but that wasn't enough to prevent algae growth. So the minimum recommendation is closer to an FC that is 5% of the CYA level (rounding up from my original 4.5%) so 4 ppm FC with 80 ppm CYA or 5 ppm FC with 100 ppm CYA. This is already lower than Ben's Min. FC for manually dosed pools, but going any lower than this may risk nascent algae growth.

I have been running 3 ppm FC with 80 ppm CYA but I do maintain 50 ppm borates so that might account for it.

Yup, the borates definitely take the edge off of algae growth as I've noticed in my own pool. This is consistent with the data in the text and in Table 18 in this link where 50 ppm seems to give a 50-70% inhibition in the rate of algae growth.

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Originally Posted by chem geek

This is consistent with the data in the text and in Table 18 in this link where 50 ppm seems to give a 50-70% inhibition in the rate of algae growth.

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Funny how we seem to read the same papers. :)