Chlorine lockup

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
granules, chlorine pucks and chlorine sticks.
pierceg8

Chlorine lockup

Postby pierceg8 » Tue 17 Feb, 2009 11:53

I have a 24k inground pool with vinal liner. Have had pool for about 16 years. Installed new liner two years ago. I use a looplock cover in winter. Have used bioguard products all this time and have had no problem til about three years ago. The problem being when I open up pool it is requiring more and more shock to get chlorine level to hold. I used 38 lbs of shock this past spring before I could get the free chlorine level to hold. where in past years it tok only three or four pounds. I do use an automatic chlorinator in which I use the 3" chlorine tabs. I have been having my water tested at a nearby pool products dealer. They say that my problem is not unique and that there has been a marked increase in the number of people with my problem. I also had more of an algae problem this past season than in past. The only thing I can think of that I do differently yhan in the past is the 3" chlorine tablets I use now called Bioguard silk tabs used to be just plain chlorine tabs. Am I doing something wrong or is there a growing problem with chlorine locking up. Appreciate any help you can provide. Jerry :(


Rayden

Postby Rayden » Tue 17 Feb, 2009 12:30

Suspect high levels of phosphate. Have you tested for phosphates?
pierceg8

chlorine lockup

Postby pierceg8 » Tue 17 Feb, 2009 12:41

Rayden wrote:Suspect high levels of phosphate. Have you tested for phosphates?

No have not checked for phosphates but will do so when I open pool this year. What could be the source of the increase in the phosphates level??
Rayden

Chlorine lockup

Postby Rayden » Tue 17 Feb, 2009 13:19

Lawn or garden fertilizers nearby is a common source, organic matter decomposing in the pool is another.
chem geek
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Chlorine lockup

Postby chem geek » Tue 17 Feb, 2009 14:02

Jerry,

Though lowering phosphates is ONE way to control algae growth and using a weekly algaecide (e.g. PolyQuat 60) also controls algae, simply maintaining the appropriate Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level will also prevent algae growth.

The problem is that you have continued to use stabilized chlorine, specifically Trichlor tabs (the type doesn't matter) and this has built up the Cyanuric Acid (CYA) level which makes the chlorine less effective. If you don't raise your FC level proportionately with the CYA level, then your pool is at much higher risk of getting algae growth which first shows up as unusual chlorine demand, then the water looks dull, then cloudy and then a full-fledge green blooom (this is typical, though other types of algae can show up as green initially).

You need to test your CYA level and should be using a good test kit. I recommend either the Taylor K-2006 kit you can get at a good online price here or the TF100 test kit from tftestkits(dot)com here with the latter kit having 36% more volume of reagents so slightly lower priced "per test".

The following are chemical rules that are independent of concentration of product and volume of pool:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

So you can see that even with a low chlorine usage of only 1 ppm FC per day, that after 6 months of Trichlor usage you add over 100 ppm CYA to the water. Unless you have a small pool with a short swim season and weekly backwashing or substantial rains and overflow, you won't be diluting the water enough to prevent this rapid CYA buildup.

In a manually dosed pool, you need to have a minimum FC of 7.5% of the CYA level or else algae can grow. Phosphates are NOT the problem. I have 2000-3000 ppb phosphates in my pool yet do not get algae because I maintain the enough FC for my CYA level. To do this, I use chlorinating liquid to prevent adding more CYA. My phosphate level is high due to 300-500 ppb phosphate in the fill water that the water district adds as a corrosion inhibitor and I have fertilized soil that sometimes gets blown into the pool in spite of the pool cover.

All of this has been known technically since at least 1974 with the chlorine/CYA relationship definitively determined in the paper shown in this link . You can learn much more about how to maintain your pool by looking at the Pool School.

If you measure your CYA level and it is high, then a partial drain/refill (or multiple smaller partial drain/refills or even continuous dilution) is in order. You should also raise the FC level using unstabilized chlorine to shock the pool and kill the nascent algae growth. I had this same problem in my own pool about 5 years ago when after using Trichlor pucks in a floating feeder in my 16,000 gallon pool, after 1-1/2 years I couldn't keep up with the chlorine demand and the water started to look dull. Prior to having the problem, I only had a 0.7 ppm FC chlorine demand (I have an opaque electric safety cover), but with my cartridge filter (so no backwashing) and a pool cover during the winter so winter rains didn't go into the pool and a 7-month swim season, I had over 150 ppm CYA (after 1-1/2 years and starting with 30 ppm CYA). I was even using algaecide, though only every other week (had I used it weekly, I could have probably gone on longer). That's when I decided to learn pool water chemistry for myself since the pool store was of no help in knowing what was really going on. Now, I spend only $15 per month on chlorinating liquid -- no algaecides or anything else except a small amount of acid every month or so.

If you want to continue to use stabilized chlorine, then you can, at extra cost, use a phosphate remover or a weekly algaecide (e.g. PolyQuat 60) to control algae, though the higher CYA will also lower chlorine's disinfection capability. Again, check your CYA level because if it's very high, you'll probably want to deal with that no matter which approach you take.

Richard
Rayden

Chlorine lockup

Postby Rayden » Wed 18 Feb, 2009 02:26

Yes, I made the assumption your cyanuric level was balanced, as you said you have had been getting your water tested at your pool shop. If it is high and has been overlooked I would suggest finding a more competent pool shop or better still invest in your own test kit as suggested above.
pierceg8

last spring water test

Postby pierceg8 » Fri 20 Feb, 2009 10:05

I dug up last springs water test results when I opened pool to check CYA level at that time. and the following is a copy of those ressults. I tend to question them now though after reading your post. Especially the CYA level of 20. This test was done after I had opened pool vacuumed to waste, shocked it. with 3lbs shock, day before. pool water was dark green.
Results:
Saturation Index 1.2
TDS 300
CYA 20
Total Chlorine 9.5
Free Chlorine 0.7
PH 8.8
Total Alkalinity 89
ADJ 83
Total Hardness 233
As a result of test pool store reccommended I use 38 lbs of shock to elimate combined chlorine and it did take this much to clear up pool and get free chlorine level to hold at 1-3. and this would only last no more than three days and I would have to shock again as free chlorine level would be gone and algae would start. During this time I was as stated before using the stabilized chlorine tabs in the auto chlorinator. After about three days I had water tested again and CYA at that time had dropped to 0. So they had me add stabilizer to correct it. Is it time for me to go to Pool School???
Jerry

chem geek wrote:Jerry,

Though lowering phosphates is ONE way to control algae growth and using a weekly algaecide (e.g. PolyQuat 60) also controls algae, simply maintaining the appropriate Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level will also prevent algae growth.

The problem is that you have continued to use stabilized chlorine, specifically Trichlor tabs (the type doesn't matter) and this has built up the Cyanuric Acid (CYA) level which makes the chlorine less effective. If you don't raise your FC level proportionately with the CYA level, then your pool is at much higher risk of getting algae growth which first shows up as unusual chlorine demand, then the water looks dull, then cloudy and then a full-fledge green blooom (this is typical, though other types of algae can show up as green initially).

You need to test your CYA level and should be using a good test kit. I recommend either the Taylor K-2006 kit you can get at a good online price here or the TF100 test kit from tftestkits(dot)com here with the latter kit having 36% more volume of reagents so slightly lower priced "per test".

The following are chemical rules that are independent of concentration of product and volume of pool:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

So you can see that even with a low chlorine usage of only 1 ppm FC per day, that after 6 months of Trichlor usage you add over 100 ppm CYA to the water. Unless you have a small pool with a short swim season and weekly backwashing or substantial rains and overflow, you won't be diluting the water enough to prevent this rapid CYA buildup.

In a manually dosed pool, you need to have a minimum FC of 7.5% of the CYA level or else algae can grow. Phosphates are NOT the problem. I have 2000-3000 ppb phosphates in my pool yet do not get algae because I maintain the enough FC for my CYA level. To do this, I use chlorinating liquid to prevent adding more CYA. My phosphate level is high due to 300-500 ppb phosphate in the fill water that the water district adds as a corrosion inhibitor and I have fertilized soil that sometimes gets blown into the pool in spite of the pool cover.

All of this has been known technically since at least 1974 with the chlorine/CYA relationship definitively determined in the paper shown in this link .

If you measure your CYA level and it is high, then a partial drain/refill (or multiple smaller partial drain/refills or even continuous dilution) is in order. You should also raise the FC level using unstabilized chlorine to shock the pool and kill the nascent algae growth. I had this same problem in my own pool about 5 years ago when after using Trichlor pucks in a floating feeder in my 16,000 gallon pool, after 1-1/2 years I couldn't keep up with the chlorine demand and the water started to look dull. Prior to having the problem, I only had a 0.7 ppm FC chlorine demand (I have an opaque electric safety cover), but with my cartridge filter (so no backwashing) and a pool cover during the winter so winter rains didn't go into the pool and a 7-month swim season, I had over 150 ppm CYA (after 1-1/2 years and starting with 30 ppm CYA). I was even using algaecide, though only every other week (had I used it weekly, I could have probably gone on longer). That's when I decided to learn pool water chemistry for myself since the pool store was of no help in knowing what was really going on. Now, I spend only $15 per month on chlorinating liquid -- no algaecides or anything else except a small amount of acid every month or so.

If you want to continue to use stabilized chlorine, then you can, at extra cost, use a phosphate remover or a weekly algaecide (e.g. PolyQuat 60) to control algae, though the higher CYA will also lower chlorine's disinfection capability. Again, check your CYA level because if it's very high, you'll probably want to deal with that no matter which approach you take.

Richard
chem geek
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Chlorine lockup

Postby chem geek » Fri 20 Feb, 2009 13:57

It doesn't take a high CYA to get algae. If the chlorine gets too low, especially close to zero, then algae can grow regardless of the CYA level. Nevertheless, unless you had significant water dilution, a CYA of 20 ppm doesn't sound right if you used Trichlor pucks as your main source of chlorine. The pool stores often do not do the CYA test correctly -- some even "invert" the number subtracting it from 100 because they don't understand the CYA scale on the test! However, I believe I know what happened and describe that below.

Now that I reread your post where you said "when I open up pool it is requiring more and more shock to get chlorine level to hold" I think I know what happened since the algae formed when the pool was closed. You probably had high CYA when you closed the pool, but you didn't maintain the chlorine level (or at least it wasn't high enough relative to CYA) when the pool was closed. That led to algae growth, but probably also bacteria growth as well. Some soil bacteria will break down CYA as food and produce ammonia (this is described technically here ). This is why upon opening and adding chlorine it looked like there was an insatiable chlorine demand. It would also explain a lower than expected CYA reading since the bacteria literally "ate" much of the CYA and it also explains the high CC with low FC readings.

If you had an ammonia test kit (from most aquarium/pet/fish stores), then it takes a chlorine PPM amount around 10 times the PPM amount of measured ammonia to get rid of it. Every 10 ppm of CYA that gets broken down by the bacteria would produce 3 ppm ammonia requiring at least 22.5 ppm (up to 30 ppm) FC to get rid of it, so this can easily create a seemingly insatiable demand. Such large amounts of chlorine can be cumulatively added and will first show up as CC, but eventually FC will hold. In practice, some of the ammonia outgasses (or is taken up by algae), but some remains so that's why you need to measure the ammonia rather than just use the CYA drop to figure how much ammonia there is to get rid of. By the way, to get rid of the CC, it does not take 10x that amount in chlorine but somewhat less than an equal amount of chlorine. The 10x rule really comes relative to ammonia, not to CC, but like much in the pool/spa industry, one person gets it wrong and then everyone follows it and it becomes dogma.

So if you still have chlorine demand and want to know how much more may be needed, then you can get an ammonia test kit. If there is a lot of ammonia, then you might consider partial drain/refill instead of chlorine to get rid of some of it -- up to you. With your high CC and very low FC, it does seem that you still have a lot of ammonia left so I suggest you measure that to decide what next to do (i.e. drain/refill vs. more chlorine).

In the future to avoid this problem, you should not let your pool go over the winter. That is, you should maintain the chlorine level (relative to CYA) to prevent algae and bacteria growth. The amount of chlorine that needs to be added on a regular basis is far less when the water gets colder. Other, more expensive, approaches you can take would be to use a PolyQuat 60 algaecide or a phosphate remover. In my own pool, I just add chlorine. With the cooler 50F water temp I only need to add chlorine about once every other week, but I have an opaque electric safety cover so there is no sun exposure.

Just so you have an idea of what happens, the following is a summary:

1) Cyanuric Acid (CYA) + bacteria ---> Ammonia (10 ppm CYA makes 3 ppm ammonia)
2) Ammonia + Chlorine (FC) ---> Monochloramine (CC) (1 ppm ammonia plus 5 ppm FC makes 5 ppm CC)
3) Monochloramine (CC) + Chlorine (FC) ---> Nitrogen Gas (1 ppm CC + 0.5+ ppm FC makes nitrogen gas)

Step 1 appears to have happened when the pool was closed when the Free Chlorine (FC) got close to zero. You currently appear to be in step 2. Only by measuring the ammonia level will you know how much further you need to go with step 2. Once you measure some FC that holds, at least overnight (i.e. not in the sun), then you'll be at step 3.

Richard
Me...

Chlorine lockup

Postby Me... » Mon 23 Feb, 2009 08:08

The best thing I have used, bar none, for combined chlorine removal is a product by Dupont called Oxone. It is Potassium Monopersulfate. If you use too much though, it could be tough to maintain a chlorine reading at all, so read the directions as to dosing carefully. It will save using tremendous amounts of chlorine which can be a lot easier on the rest of the chemistry too.
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Chlorine lockup

Postby chem geek » Mon 23 Feb, 2009 15:29

Me... wrote:The best thing I have used, bar none, for combined chlorine removal is a product by Dupont called Oxone. It is Potassium Monopersulfate. If you use too much though, it could be tough to maintain a chlorine reading at all, so read the directions as to dosing carefully. It will save using tremendous amounts of chlorine which can be a lot easier on the rest of the chemistry too.

In the past, I've talked to Dupont about Oxone which is just the trade name for MPS used in virtually all non-chlorine shock products (they make the MPS used in almost all of these products). They say it is much better at preventing chloramine formation than removing already existing chloramines. Nevertheless, even if it did remove chloramines, chlorine does that as well, especially in a situation where it is monochloramine from ammonia (as opposed to an organic chloramine where MPS might be better). Chlorine (i.e. chlorinating liquid or unscented bleach) is vastly less expensive than MPS.

In terms of oxidizing equivalence, one pound of non-chlorine shock (which is a triple salt, one component of which is MPS) is the same as 50 fluid ounces of 6% bleach, 24 fluid ounces of 12.5% chlorinating liquid, 5 ounces weight of 65% Cal-Hypo, 3.5 ounces weight of Trichlor, or 5.8 ounces weight of Dichlor (dihydrate). One pound of non-chlorine shock bought in bulk here is $56.95/24 = $2.37 while 24 fluid ounces of 12.5% chlorinating liquid is around $3.65*24/128 = $0.68; 50 fluid ounces of 6% bleach is around $1.25*50/96 = $0.65; 5 ounces of 65% Cal-Hypo is $59.95*(5/16)/24 = $0.78. The non-chlorine shock is over 3 times as expensive to produce the same result.

The problem here is not necessarily only Combined Chlorine (CC) in this pool. I strongly suspect there may be ammonia leftover as well. Though either chlorine or MPS could be used to oxidize this ammonia, if there is a lot of it then a partial drain/refill might make more sense. That's why I suggested getting an ammonia test kit to see how much there is left to get rid of.

Richard

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