CYA in a Bromine Pool

[PoolDoc]

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

[aylad]

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

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

[chem geek]

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

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.

[CarlD]

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.

[chem geek]

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.

[CarlD]

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.

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

[waterbear]

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

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

[CarlD]

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