Help with 'special needs' pool

[isrmomof3]

Hey folks.

I have just recently discovered this and the PF site and begun educating myself on pool chemistry. Until now, I've just relied on the advice of my local pool store.....now that I understand more about what's actually going on with my water, I'm not sure I was getting good advice.

In any case, I live in southern Arizona and I have a 'special needs' pool because of my unique bather load. I am a nationally certified survival swim instructor and I have anywhere from 15-30 infants and small children in my pool EVERY DAY, ranging in age from 6 months to 6 years, all within a 2 to 4 hour block of time.

I had my water tested on Monday and here's what I had:

FC: 2
pH: 7.2
TA: 100
CH: 350
CYA: 100
I have a 22,000 gal inground plaster pool with attached spa, sand filter, corona discharge ozonator, solar heating & solar blanket. I keep the water temp between 85-88.

I now know that based on my CYA level, my FC needs to be WAY higher than it is and have been adding the granular chlorine (calcium hypochlorite) to raise the FC. My FC is now around 7ppm.

Here are my questions:

Can someone tell me why high CYA dictates a higher level of FC? I don't understand that relationship....and my hubby is skeptical.

I JUST purchased a 50 lb. bucket of trichlor, and have read that trichlor is bundled with CYA, which will cause my CYA to go even higher.....is there any way I can continue to use it with my already too-high CYA? The label says it is 99% trichlor, 1% other, and total deliverable chlorine is 90%. I'd sure hate to shelf $150 in chlorine...

In looking at my also brand-new 50 lb. bucket of Bioguard CLC2 (what they sold us to use to shock the pool), it's calcium hypochlorite 47% and other ingredients 53% and I'm wondering if there are any CYA or other issues with that product that I need to be aware of...

I've also been following the store's dosage instructions for shocking with the CLC2, which is 1 lb per 10K gallons, so I've been using 2 lbs for my 22K gal pool. How long does the FC need to remain high in order for the "shock" to occur? Is it just that it needs to get up to that level, and then I can let it go back down, or does it need to stay there for a period of time? I read somewhere that with my CYA, I need to obtain 25ppm FC for shock. This seems like a scary high number to me. How long do bathers need to stay out of the pool at that level, especially considering that most of my bathers are 4 and under??

Any other things that I need to know about, given my unique bather load?

Thanks to any and all that take the time to reply! I'm finally beginning to understand the chemistry and it's nice to feel like I might be in control again...

 

[JohnT]

Think of CYA as a suit of armor for your chlorine. It protects it from sunlight degradation, but it also slows it down and makes it less active.

Your CH is already high enough, so using Cal-hypo is going to cause problems eventually.

Many medical and health professionals are moving toward the conclusion that infants are simply unsafe in pools because of the high risk of fecal contamination, even with swim diapers. Your high bather load in a short time dictates that your sanitizer needs to be very active to avoid transfer of viruses or bacteria between bathers. You need a no exceptions policy of no sick kids or their siblings in the pool. I don't know if you can work it, but infants last would reduce the risk of exposure for the older children.

You may want to consider a salt water chlorine generator. Your students will appreciate the comfort of the saltwater, and your chlorine level will remain more constant without the daily addition of any chemicals.

 

[The Mermaid Queen]

Welcome to TFP!!

I will embed a few answers (not too technical, I'm afraid) below. Those more knowledgeable that I will be along shortly!

Hey folks.

I have just recently discovered this and the PF site and begun educating myself on pool chemistry. Until now, I've just relied on the advice of my local pool store.....now that I understand more about what's actually going on with my water, I'm not sure I was getting good advice.

In any case, I live in southern Arizona and I have a 'special needs' pool because of my unique bather load. I am a nationally certified survival swim instructor and I have anywhere from 15-30 infants and small children in my pool EVERY DAY, ranging in age from 6 months to 6 years, all within a 2 to 4 hour block of time.

I had my water tested on Monday and here's what I had:

FC: 2
pH: 7.2
TA: 100
CH: 350
CYA: 100
I have a 22,000 gal inground plaster pool with attached spa, sand filter, corona discharge ozonator, solar heating & solar blanket. I keep the water temp between 85-88.

I now know that based on my CYA level, my FC needs to be WAY higher than it is and have been adding the granular chlorine (calcium hypochlorite) to raise the FC. My FC is now around 7ppm.

Here are my questions:

Can someone tell me why high CYA dictates a higher level of FC? I don't understand that relationship....and my hubby is skeptical.

The short answer is that while the CYA helps to keep the chlorine in your pool longer so it can do its job sanitizing the water, it also decreases the effecticeness of the chlorine. That is why people who use trichlor for a long time with great results will suddenly start having problems, even though the numbers look the same as always.

I JUST purchased a 50 lb. bucket of trichlor, and have read that trichlor is bundled with CYA, which will cause my CYA to go even higher.....is there any way I can continue to use it with my already too-high CYA? The label says it is 99% trichlor, 1% other, and total deliverable chlorine is 90%. I'd sure hate to shelf $150 in chlorine...

Can you return it? That'd be your best option if you have not opened it.

In looking at my also brand-new 50 lb. bucket of Bioguard CLC2 (what they sold us to use to shock the pool), it's calcium hypochlorite 47% and other ingredients 53% and I'm wondering if there are any CYA or other issues with that product that I need to be aware of...

I've also been following the store's dosage instructions for shocking with the CLC2, which is 1 lb per 10K gallons, so I've been using 2 lbs for my 22K gal pool. How long does the FC need to remain high in order for the "shock" to occur? Is it just that it needs to get up to that level, and then I can let it go back down, or does it need to stay there for a period of time? I read somewhere that with my CYA, I need to obtain 25ppm FC for shock. This seems like a scary high number to me. How long do bathers need to stay out of the pool at that level, especially considering that most of my bathers are 4 and under??

With a CYA of 100, the shock level of 25 SEEMS LIKE the shock level of 10 in a lower CYA pool. So while it is a big number, the effect is much smaller due to the CYA. When Shocking your pool, you should test for CC first. If you don't have any CC (though with babies, you WILL have CC ) there is no need to shock. You should keep the level up until the CC clears.
You should add your chlorine at night so it can work without having to fight with the sun, though with your situation and your CYA, I think I would test and add bleach (or shock the pool) as soon as the pool was clear for the day. With a CYA that high, the recommended FC level is 8-15. At these levels, it is safe for swimming, since as I mentioned the CYA decreases the effects of the Cl.

Any other things that I need to know about, given my unique bather load?

Thanks to any and all that take the time to reply! I'm finally beginning to understand the chemistry and it's nice to feel like I might be in control again...

 

[chem geek]

The chlorine/CYA issue is controversial because some of the manufacturers and distributors of CYA-based products, such as Trichlor and Dichlor, don't believe the relationship applies to "real pools". Essentially what happens is that the active disinfecting form of chlorine, called hypochlorous acid that I'll just call Cl for short, combines with Cyanuric Acid (CYA) to form new compounds (called chlorinated isocyanurates) that I'll just call Cl-CYA for short. Cl is very sensitive to ultraviolet (UV) radiation from sunlight and half of it will break down in direct noontime sun in around 35 minutes. The Cl-CYA also breaks down, but it takes longer -- about 8.4 hours for half of it to degrade in direct noontime sun. There is an equilibrium between the free and effective Cl and the bound and protected Cl-CYA where most of the chlorine in the water is in the Cl-CYA form, not the Cl form. When you measure Free Chlorine (FC), you are measuring BOTH the Cl and Cl-CYA forms (as well as hypochlorite ion we haven't talked about). The controversy isn't really about whether these products exist nor their relative amounts -- the controversy is over whether Cl-CYA is effective as a disinfectant and in preventing algae. There are studies that appear to go both ways -- studies funded by the industry show that CYA doesn't matter while independent scientific studies show that Cl-CYA is not effective while Cl is.

Technical details about this may be found at this thread while the main study the industry uses to claim that CYA doesn't matter and that only FC is important (and my analysis of that study) may be found at this thread. Regardless of the technical details, the reality is that there are many users on multiple pool forums who have had green algae develop in their pools and in every single instance it was the result of either having no chlorine or having an FC level that was too low relative to the CYA level. Ben Powell created this Best Guess CYA chart based on his experience with hundreds (if not more) pools and not one pool that has been maintained according to this chart has developed green algae. We have since found that the Max column must be followed to prevent mustard/yellow algae and when I calculated the actual chemistry behind all of this I found that Ben's chart tracked the chemistry very closely where his Min and Max columns are very similar to the 0.03 and 0.07 columns in this chart that I created.

It is true that you can have high CYA levels and low FC levels and not get algae if you use a weekly algaecide, usually PolyQuat 60, and that is what most manufacturers and pool stores try to sell. However, maintaining sufficient chlorine levels relative to CYA levels will also keep away algae. As for disinfection, it takes an extremely small amount of disinfecting chlorine to kill most bacteria, but with your higher bather loads it would make sense to play it safer with higher levels that would prevent algae on their own and would kill pathogens faster.

 

[tpg]

Nice post Chem Geek,

I have to tell you, I started reading all the charts and study analysis and my brain started to hurt! I haven't seen numbers like that since I was reviewing federal government budget analysis. That has been a few years ago.

Anyways, thanks for posting this info, I will reread it in the morning when I am awake, with a fresh cup of coffee and my hard headed brain is working some what properly.

 

[isrmomof3]

Thanks for all the great information!

I do have very strict safety protocols about what my swimmers have to wear (don't EVER let a child wear a any kind of disposable swim diaper in your pool ~ they must wear TWO layers of plastic pants) and strict illness exclusion policies.

Would you all say that liquid chlorine is the fastest delivery method? How long do you think that it takes for the granular chlorine to disperse in the water? I'm thinking that I may want to switch to liquid so that I can get up to shock levels faster....

Also, I had been seriously considering a SWG.... How effective are they at maintaining higher levels of chlorine at my high rate of consumption? Would a SWG really be able to keep up with my high bather load?

I'm so disappointed that I never questioned the pool store's advice before. Hubby took a sample in yesterday and they told him that liquid chlorine is the "dirtiest" form of chlorine (along with the implication of course that it's a sub-standard product) and that our water is fine with CYA levels of 100ppm. I just told him that it IS fine - we just need to use twice the amount of chlorine!

Thanks for helping me learn all this stuff!

 

[JohnT]

Also, I had been seriously considering a SWG.... How effective are they at maintaining higher levels of chlorine at my high rate of consumption? Would a SWG really be able to keep up with my high bather load?

You can get a larger cell and/or use a longer pump run time to increase the chlorine production. Many people still shock with liquid even with a SWCG just because it save cell life. Post a question in the SWCG forum or try to track down PoolSean's email address. He's a customer service(I think) guy for a major SWCG manufacturer.

 

[JasonLion]

I am sure you can find a SWG appropriate for your needs. SWGs are available in various capacities. Manufacturers typically rate them in terms of pool size, but for your situation that measurement is misleading. Instead look at the rate at which they can produce chlorine and compare that to how much chlorine you are adding now. A residential SWG might be able to produce between 1/2 and 2 lb of CL a day. Commercial models can produce *far* more than that. It may take a little more digging to locate these numbers for specific models. Some of the better manufacturers will be happy to talk to you about your needs and then make a specific proposal. Keep in mind that the SWG is only able to produce CL while the pump is running. If you leave your pump on all the time you will be able to produce more chlorine than if you only run the pump four hours a day.

Another factor to keep in mind is that a SWG pool is normally run at a higher CYA level than a bleach pool and yet has about the same level of FC. That means that they lose less CL to sun light. This works because the SWG produces CL continuously. A typical bleach approach requires adding enough to still meet your target CL level after losing 50% to sun light. The net effect is that a SWG pool typically uses less total CL. Some people believe that a SWG can additionally run at lower CL levels because a super chlorination effect in the cell destroys CC in ways not seen in bleach pools.

 

[waste]

John, excellent analogy!!

Joined: 04 Apr 2007
Posts: 92
Location: SW Indiana

PostPosted: Fri May 11, 2007 12:54 pm Post subject: Reply with quote Back to top
Think of CYA as a suit of armor for your chlorine. It protects it from sunlight degradation, but it also slows it down and makes it less active.

(I don't know where the other stuff came from - other than the quote, but I'll take it for my first try )
Jason, exellent advice/ info too!!