Superchlorination

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
granules, chlorine pucks and chlorine sticks.
sparkwatercleaner
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Superchlorination

Postby sparkwatercleaner » Sun 16 Dec, 2007 20:54

I use chlorine tabs as a sanitizer for my pool. They also add stabilizer.
I bought liquid chlorine (sodium hypochlorite), so that I can shock my pool without adding stabilizer.

-If I add the liquid chlorine in the afternoon/night, will I be able to swim the following morning???

-Will the stabilizer that is continuously added to the pool by the tabs make the high chlorine levels stay longer in the pool (if so, how much?)???

-My pool has 10 gallons. Is it ok if I add 1 gal of liquid chlorine to shock?? (I can't say for sure how much combined chlorine is in the pool because where I live there are not any test kits that measure it).

-Will the shock affect paint???

-If I add the liquid chlorine through the skimmer, will it affect the filter??? May I add it directly to the pool instead??? Do I have to dillute it???


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Postby chem geek » Sun 16 Dec, 2007 23:42

You shouldn't need to shock the pool unless you measure Combined Chlorine (CC) or there was some sort of accident (discharge from young swimmers, for example) or your pool is developing algae (turning dull or cloudy or green). One gallon of 12.5% chlorinating liquid in 10,000 gallons would raise the Free Chlorine (FC) level by 12.5 ppm. If you have CYA in the water already, then that's not too high a shock level and in fact if your CYA level is high then it's not high enough for shocking. But again, you don't need to shock unless necessary.

It may take a full day for the chlorine to drop if it's exposed to sunlight (it will drop quickly if you're fighting algae).

You should get a Taylor K-2006 (not 2005) test kit if you don't already have one and should measure your CYA level to make sure it's not too high. If you are using mainly stabilized chlorine, then the CYA may be high which can lead to algae if you don't use an algaecide or phosphate remover regularly or maintain a higher FC level. You can get a kit at a good price here or you can get the TF100 test kit from tftestkits(dot)com here that has 36% more volume of reagents so is effectively the same price.

The stabilizer in your pool does make the chlorine last longer in terms of not breaking down as quickly from sunlight. How long depends on the amount of CYA and the intensity of the UV rays of sunlight. At peak summer, CYA in the range of 30-50 ppm has the FC drop by less than half its value over the day -- without any CYA the FC would drop in half in less than an hour. At 60-80 ppm CYA, the FC may take 2-3 days to drop in half, but higher CYA levels can be harder to manage if you aren't careful (re: algae as I mentioned above).

The shock will not affect a painted pool. It's stronger than normal, but not THAT strong.

Do not add the chlorine to the skimmer. It is better to add it slowly over a return flow so that it thoroughly mixes in the pool and the deep end is better, especially if you have a floor drain. Do not add it too quickly or else the chlorine can sink to the bottom before mixing (it's denser than water). You do not need to dilute it if you pour it slowly enough to see that it is mixing with the return flow and not just sinking. For extra safety, you can brush in that area after adding it.

Richard
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Postby sparkwatercleaner » Mon 17 Dec, 2007 09:22

Well, thanks for your quick reply Richard.

The major problem I have with test kits is that they aren't sold anywhere here in Argentina. The only ones you find just test free chlorine and ph and, if you are extremely lucky like me, you may find one that tests Total Alk.

So, I want to shock because I am starting to smell chlorine odor, which means choramine levels are rising, but I don't know exactly how much.

I don't know either how high are stabilizer levels. It may help to know that I vacuum to waste once every week, so 3 inches of the pool water are replaced weekly. I suppose CYA levels are OK.

The chlorine I bought is sodium hypochlorite, and its label states it has 111 grams of chlorine per liter. That would be 10% or 11% active chlorine. It says an everyday dose should be 2 liters for my pool, almost 2/3 of a gallon.

Do you still recommend me to add a gallon for my pool, and that it will rise chlorine levels up to 10 ppm???
If CYA levels are within range, how much will it take for the chlorine to break down in sunlight???

Thanks in advance.
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Postby chem geek » Mon 17 Dec, 2007 13:51

That's too bad you can't get a decent test kit. Since your pool is outdoors, it is unusual to have chloramines or other combined chlorine because the UV in sunlight helps to break them down. I suspect that your CYA level might be on the high side since that causes more of the smellier disinfection by-products to form (dichloramine and nitrogen trichloride), but that's just a guess.

At any rate, you can certainly add a gallon of that chlorinating liquid you have to the pool. Most important is to keep the pool uncovered after you've added the shock. It needs to air out for the reactions to proceed and the exposure to sunlight should help as well.

You might still check out the tftestkits(dot)com and write to them since I know they have shipped to Canada and might be able to ship to you, though the postage and duty fees won't be cheap.

As for how long it will take for the chlorine level to drop, I would say about one or two days. You can still test it with your basic Free Chlorine test though a DPD (red color) test will bleach out at high chlorine levels above 10 ppm so be careful about that. An OTO (yellow color) test won't bleach out but doesn't separately measure Free and Combined chlorine very well. The best test is the drop-based (i.e. count the drops) FAS-DPD chlorine test.

Since you've probably got a lot of CYA in the water, you can swim in it even if the FC is 10 ppm or below. The CYA significantly reduces the effective disinfecting chlorine (hypochlorous acid) concentration. 10 ppm FC with 50 ppm CYA is equivalent to 0.2 ppm FC with no CYA in terms of oxidation, disinfection power.

Richard
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Postby sparkwatercleaner » Tue 18 Dec, 2007 17:40

So, you say 1 gallon will still shock the pool?

I've read that if you add chlorine but you don't reach the breakpoint oxidation it would be a problem. Why?

You also say that CYA levels is high although 3 inches of the pool's water (almost 800 gallons) are replaced weekly?

Thanks for your suggestion with the test kits. They ARE expensive to me with their normal price ($50) as here it would be three times more expensive (50 dollars --> 150 pesos), plus all I would have to pay for shipping, etc.
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Postby chem geek » Tue 18 Dec, 2007 19:40

One gallon of 12.5% chlorinating liquid in 10,000 gallons will raise the Free Chlorine (FC) by 12.5 ppm which should be enough to shock unless your CYA level if high. If your pool is exposed to sunlight, then I doubt you have many chloramines. You might just be smelling it on your skin which is normal since sweat has ammonia like compounds (urea) and combines with chlorine to form chloramine. That doesn't mean they are in large quantities in the pool itself. If you have the pool covered, I suggest keeping it uncovered for a few hours and that should take care of the smell.

What you read about breakpoint refers to fully oxidizing ammonia and it is true that if you do not have enough chlorine, then you can form monochloramine. However, if you use too much chlorine, then you can actually form more of the harder-to-remove dichloramine and nitrogen trichloride. Normally you don't have to worry about any of this since the UV radiation in sunlight breaks down monochloramine and most other combined chlorines. However, if your CYA level is very high, then breakpoint of ammonia by chlorine can be much slower so if the pool is covered or not exposed to sunlight then that could lead to smelly monochloramine.

800 gallons replaced weekly is a dilution of 800/10,000 = 8% per week which sounds like a lot, but it really depends on the amount of chlorine you are adding to your pool with the Trichlor pucks/tabs. Let's say you are adding 3 ppm FC per day. That adds 1.8 ppm to CYA per day so 12.6 ppm per week. So the steady state is reached when:

0.08 * x =12.6

x = 157.5 ppm

That is, you will continue to build up CYA until it is over 150 ppm at which point the dilution to 0.92 * 150 = 138 ppm plus the weekly addition of 12.6 ppm to 138 + 12.6 = 150.6 ppm is around a steady state situation.

If your CYA level is indeed high, then the pool may not have enough chlorine in it. To keep away green algae, you need a minimum FC that is 7.5% of the CYA level. You can have a lower FC level, perhaps 3% of the CYA level, if you use an algaecide (such as PolyQuat 60) or a phosphate remover, but those are extra expenses that are normally not needed.

If you used chlorinating liquid as your regular source of chlorine, then you wouldn't need to be adding pH Up products which I assume you need to add regularly as Trichlor is very acidic. You can automate chlorine dosing with The Liquidator (assuming you can get this product where you are) which is also discussed in this thread on another forum. In your situation with regular 8% weekly solution, you could alternate between using chlorinating liquid and sometimes adding CYA either directly or via Dichlor powder or Trichlor. But you really should get a CYA test kit otherwise you're in the dark with regards to the disinfection level in your pool. The ratio of FC to CYA roughly determines the disinfection level and this chart gives some values of FC vs. CYA for different disinfection levels.

Richard
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Postby sparkwatercleaner » Tue 18 Dec, 2007 20:58

Richard,

Thanks, thanks and lots of thanks for your help. I can see you spent quite a lot of time to help me. I really appreciate it.

I'm really annoyed because pro test kits aren't sold anywhere here, I've searched. But forget about it, it will be useless to keep on trying to find a solution. Among people I know, I'm one of the most dedicated pool owners in here.

I've added 1 gal of liquid chlorine and the test kit shows 11 ppm more or less (free chlorine). I'll leave the filter running all night long.

Thank you for your useful calculations of CYA levels. So, no one can use trichlor tabs for regular sanitation for ever??? No one (the pool guy, shop,etc) ever told me there would be problems with stabilizer.

Talking about chloramines, I've read in various web pages that they may be present in every pool, and that's why one would have to shock. Also, I've read that a shock must be done weekly during the swimming season (which would be right now in Argentina). Also, I've read that chlorine is broken down by UV rays, but chloramines don't, and that they should be broken apart with some chemical.


(From Wikipedia)

Situations where NH2Cl should be removed

Aquarium owners must remove the chloramine from their tap water because it is toxic to fish. Aging the water for a few days removes chlorine but not the more stable chloramine, which can be neutralised using products available at pet stores.

Many animals are sensitive to chloramine and it must be removed from water given to many animals in zoos.

Chloramine must also be removed from the water prior to use in kidney dialysis machines, as it would come in contact with the bloodstream across a permeable membrane. However, since chloramine is neutralized by the digestive process, kidney dialysis patients can still safely drink chloramine-treated water.

Home brewers use reducing agents such as sodium metabisulfite or potassium metabisulfite to remove chloramine from brewing liquor as it, unlike chlorine, cannot be removed by boiling (A.J. DeLange). Residual sodium can cause off flavors in beer (See Brewing, Michael Lewis) so potassium metabisulfite is prefered.

In swimming pools, chloramines are formed by the reaction of free chlorine with organic substances. Chloramines, compared to free chlorine, are both less effective as a sanitizer and more irritating to the eyes of swimmers. When swimmers complain of eye irritation from "too much chlorine" in a pool, the problem is typically a high level of chloramines, caused by too little chlorine in relation to the amount of organic matter. Pool test kits designed for use by homeowners are sensitive to both free chlorine and chloramines, which can be misleading.


Anyway, thank you for your help!

Last question, if my CYA levels are REALLY high, chlorine will take some days to break down and reach 2 ppm, right? I've also read that, if it is unstabilized, it will last an hour in the pool. So, depending on how much it takes for the FC to drop, I'll get an idea of CYA levels. Do you know any rate? For example, 5 hours-->50ppm, etc...(not real example).
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Postby chem geek » Wed 19 Dec, 2007 00:09

You can certainly use Trichlor on occasion, but if you use it as your sole source of chlorine then you HAVE to use either an algaecide or a phosphate remover or else you will risk getting algae. Your pool will also be less sanitized. Technical details about all of this are at this post on another pool forum you may be more interested in. If you search the web, you'll find plenty of scientific studies that show chlorine's reduced effectiveness in the presence of CYA, but the industry tends to downplay that.

Basically, for every 1 ppm FC added with Trichlor it also adds 0.6 ppm to CYA. Also, for every 1 ppm FC added with Dichlor it also adds 0.9 ppm to CYA. Finally, for every 1 ppm FC added with Cal-Hypo it also adds 0.7 ppm to Calcium Hardness (CH).

With bleach, chlorinating liquid, and Lithium hypochlorite, you don't get any CYA nor CH increase, but it does add extra salt of 0.8 ppm for every 1 ppm FC, but that's not a big problem -- especially with your regular dilution (which dilutes a larger salt level so can keep up with the additions).

Chloramines are very susceptible to UV radiation. If you do a search on "chloramines UV" you will see that UV is very effective at destroying chloramines. If you do a search on "chloramines sunlight" then you'll find mixed sources, but even the ones that say they are stable still show decay of "at most 0.2 ppm per peak sunlight hour" -- just slower than free chlorine, but still decaying. Also, the better air circulation outdoors also helps as monochloramine is volatile, which is why you smell it (higher chloramines of dichloramine and nitrogen trichloride are even more volatile and smell worse and are more irritating). Generally speaking, outdoor pools exposed to sunlight and air circulation don't need regular shocking unless the bather loads are high.

And most important of all is that if you maintain the proper FC level, then chloramines are CONSTANTLY undergoing breakpoint and getting "shocked" by the chlorine. However, if your CYA level is very high, then this breakpoint process is slowed way down so chloramines could build up.

Yes, if CYA is really high, then the FC takes longer to drop in sunlight as more of it is attached to CYA and more stable in sunlight plus CYA shields the lower depths of the pool from the UV rays by absorbing it directly. And yes, if there is no CYA in the water then half of the FC can break down in a half hour. So you WANT some CYA, just not too much. 30-50 ppm is a usual amount, but in very hot climates you could manage more IF you are careful to never let your FC level drop too low as you need to maintain an absolute minimum FC of 7.5% of the CYA level to prevent algae (up to 3000 ppb phosphate levels -- higher phosphate levels need more chlorine, but then it's better to reduce phosphate levels if they are that high which is quite rare).

Estimating CYA levels based on FC drop is going to be VERY rough, but generally speaking if you lose around half of your FC in one mid-summer day (that would be now, for you), then you've probably got around 20-30 ppm CYA. If you lose only a quarter of the FC in a day, then you've got around 50-60 ppm and if you use less than that, then you've got more CYA but it's really hard to know how much. Also, this assumes there is no loss from other sources -- so not swimming in the water. You may have other organic demand or even a pending algae bloom that can consume chlorine. To check for that, see how the FC drops overnight when the sun isn't shining. If you see more than a 1 ppm FC drop, then you've got something consuming chlorine in your pool -- normally you should see minimal drop overnight. If your chlorine loses only a little more during the day than at night, then you've got a heck of a lot of CYA in the water.

Richard
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Postby sparkwatercleaner » Wed 19 Dec, 2007 10:03

Ok, I've read about chloramines and agree.

But I've read various things about CYA. I've read that it takes years for it to reach 100 ppm with dichlor and trichlor. Also, I've read good pool owners don't have CYA problems as regular backwashing makes some water be replaced. And others say not to use dichlor and trichlor for regular sanitizing. If I use them regularly, would I have to dilute 1/2 of the pool every month??? More often or not??? I'm confused...

My tabs are called "triple action", as they add chlorine, stabilizer, algaecide and flocculant. And I have lots of them so I would like to keep using them. Up to now, I've had no problem and FC levels were 1 PPM at all times while using them. Also, I add dichlor once a week.

Question: At 100 ppm CYA, wil FC readings be the same as with less or none CYA???
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Postby sparkwatercleaner » Wed 19 Dec, 2007 12:43

Another question:

If CYA is too high and I therefore need to keep a higher FC level in my pool, will it cause any problem as it is higher than normal??? For example, If my pool demands 6ppm FC because CYA is too high, would it be the same as 6ppm FC with no CYA??? (I ask beacause the harm it may do to swimmers)

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