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AAS

Can';t Hold Chlorine

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We can't keep our chlorine. It doesn't get combined but keeps going to 0 free and 0 combined. All our other numbers are in line. We double shocked and by am both free and combined were 7.6 By 2:30pm our numbers both dropped to 4.2 and tonight we are almost at 0! Are automatic chlorinator is also turned ALL the way up and we have 3 sticks int the skimmer basket. What is going on?

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sounds like a stabilizer block, too much cyanuric acid. The only way to fix is to dump 1/2 the water and refill.

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First question, how are you testing, strips or drop kit?

What is your CYA level?

If you shock at night does the chlorine hold until moring? If it does and the chlorine is disappearing during the day it sounds like you don't have enough stabilzier in the water and the chlorine is being burned off by the sun. You need about 30 to 50 ppm to keep the chlorine in the pool during the day. If you could post a full set of test numbers for FC, TC, pHk, ALK, CH and CYA done with a reagent test and NOT with test strips it would be helpful in figuring out what is going on in your pool.

sounds like a stabilizer block, too much cyanuric acid. The only way to fix is to dump 1/2 the water and refill.

This would NOT cause the FC and CC to drop to 0 ppm! And the proper term is 'chlorine lock' which is what pool stores tell you you have when they don't have a clue!

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We can't keep our chlorine. It doesn't get combined but keeps going to 0 free and 0 combined. All our other numbers are in line. We double shocked and by am both free and combined were 7.6 By 2:30pm our numbers both dropped to 4.2 and tonight we are almost at 0! Are automatic chlorinator is also turned ALL the way up and we have 3 sticks int the skimmer basket. What is going on?

You likely have no stabilizer in the water. Take a sample of water to a pool store, and have it tested. That should fix the problem.

Lew Akins www.lewakins.com

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You likely have no stabilizer in the water. Take a sample of water to a pool store, and have it tested. That should fix the problem.

Lew Akins www.lewakins.com

I have taken a sample they have NO idea

TDS 0

CYA 40 pH 7.5

alk 141

The store is the one who has been testing my chlorine - they don't know why we cant keep it

I have taken a sample they have NO idea

TDS 800

CYA 40 pH 7.5

alk 141

The store is the one who has been testing my chlorine - they don't know why we cant keep it

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You may have a chlorine demand caused by something that got into your water. Ammonia will cause a large chlorine demand. You will find ammonia in many household cleaners, fertilizers, etc. The only way to overcome the demand is to blast it with shock. Most chem companies suggest 5 lbs of hypochlorite per 10000 gallons to overcome the demand.

Consider this as well...You say that your chlorinator is all the way open. Is it possible that your chlorine level is too high? When this happens, the color from the test strip or reagent can get bleached away, leading you to believe that you have no chlorine, when in fact there is too much. This false reading is much more common than the demand problem above.

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ok, I have a few more questions to try and get a handle on this. First, how is the pool store testing? Strips or reagents? If they are using strips or DPD testing it is possible that the test is bleaching out due to high chlorine levels. If they are using FAS-DPD titration testing for chlorine then the reported results are accurate. You can check yourself by getting a cheap OTO test kit for chlorine(turns yellow) . It is not very accurate but it will not bleach out. It will only show TC but if you test when the other readings are showing no chlorine and it turns very yellow to orange or brown that means you have high chlorine levels and the other test is bleaching out. If the other test for FC is a DPD test the pool water sample can be diluted to get a reading.

Next question, did you just open the pool and have you had this problem since opening. If so, what was your CYA level when you closed the pool. CYA can be biodegraded by anerobic bacteria in a closed pool. If you opened the pool and the CYA was lower than when you closed it this is probably what happened. The bacteria excrete ammonia compounds and urea. This will create a HUGE chlorine demand in the pool until they are burned off. If this is the case keep hitting it with chlorine morning, noon and night until the chlorine is holding!. It can take a LOT of chlorine and liquid chlorine is the best choice for this.

Your current CYA level of 40 ppm is fine and the chlorine is NOT getting burned off by the sun.

Hope this is helpful.

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ok, I have a few more questions to try and get a handle on this. First, how is the pool store testing? Strips or reagents? If they are using strips or DPD testing it is possible that the test is bleaching out due to high chlorine levels. If they are using FAS-DPD titration testing for chlorine then the reported results are accurate. You can check yourself by getting a cheap OTO test kit for chlorine(turns yellow) . It is not very accurate but it will not bleach out. It will only show TC but if you test when the other readings are showing no chlorine and it turns very yellow to orange or brown that means you have high chlorine levels and the other test is bleaching out. If the other test for FC is a DPD test the pool water sample can be diluted to get a reading.

Next question, did you just open the pool and have you had this problem since opening. If so, what was your CYA level when you closed the pool. CYA can be biodegraded by anerobic bacteria in a closed pool. If you opened the pool and the CYA was lower than when you closed it this is probably what happened. The bacteria excrete ammonia compounds and urea. This will create a HUGE chlorine demand in the pool until they are burned off. If this is the case keep hitting it with chlorine morning, noon and night until the chlorine is holding!. It can take a LOT of chlorine and liquid chlorine is the best choice for this.

Your current CYA level of 40 ppm is fine and the chlorine is NOT getting burned off by the sun.

Hope this is helpful.

If your CYA is too high the chlorine will not release and won't meet the demand as well.

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If your CYA is too high the chlorine will not release and won't meet the demand as well.

This was already covered at the beginning of this thread when someone mentioned 'chlorine lock'. This would NOT explain the FC testing at 0 ppm since chloroisocyanurates DO test as FC!

Anyway AAS stated that his/her CYA was at 40 ppm! This is certainly NOT going to overstabilze the pool and is, in fact, right in the middle of the 30-50 ppm recommended range for CYA!

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If your CYA is too high the chlorine will not release and won't meet the demand as well.

This is not true. When chlorine in water (hypochlorous acid, HOCl) is in the presence of Cyanuric Acid (CYA) it forms several chlorinated cyanurate species of which HClCY- (where "CY" is the cyanurate portion) is the dominant species. The reaction HClCY- + H2O --> H2CY- + HOCl has a half-life (at 77F) of 4.08 seconds. That means that it only takes about 4 seconds for half of the Total Chlorine (TC) to be made available as Free Chlorine (FC) as the Free Chlorine gets used up. In other words, the CYA acts as a buffer or reserve of chlorine and releases that reserve quickly in terms of normal demand.

On the other hand, for the purposes of disinfection and oxidation, it is the concentration of the active form of chlorine, hypochlorous acid (HOCl) that is important. It is this concentration that is significantly reduced in the presence of CYA. At a pH of 7.5, a rough guide that is reasonably accurate when the CYA ppm is more than 5 times the FC ppm is that CYA reduces chlorine's active concentration, and therefore its effectiveness, by 75% of the CYA level measured in ppm. So with a CYA level of 30 ppm, the effectiveness of chlorine is reduced by a factor of 0.75*30 = 22.5 while at a CYA level of 100 ppm the effectiveness of chlorine is reduced bby a factor of 0.75*100 = 75. So, three times the CYA means 1/3rd of the chlorine effectiveness. Or put another way, you need three times the FC level with a CYA of 100 than with a CYA of 30 to have the same equivalent disinfection and oxidizing capability. So while the relatively large chlorine reserve means that there is lots of chlorine around to kill lots of bugs and algae (i.e. there is a large "capacity"), with high CYA and not high enough FC the active chlorine concentration may not be high enough to kill such bugs and algae at a rate faster than they reproduce (i.e. there is not enough "power" or "rate").

So having a high level of CYA does not prevent the chlorine from getting released. It just combines with too much chlorine leaving too little active chlorine. Though this can be compensated by higher FC levels, such higher FC levels result in higher chlorine usage since the breakdown from sunlight is related to this total FC level. I don't want to go into the details here, but I have lots of graphs and details about all of this on another forum, but this forum's guidelines refers to compeitiveness and preventing other forum owners from posting here. I'm not an owner of the other forum, but providing a link to it might tick off this forum's owners -- I don't know.

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I have taken a sample they have NO idea

TDS 0

CYA 40 pH 7.5

alk 141

The store is the one who has been testing my chlorine - they don't know why we cant keep it

Are you sure your chlorinator is producing chlorine? Cuz i don't know any model which would work with 800ppm salt level.

Or you are talking about chlorine dosing system?

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Hi,

If you have a salt pool, there is absolutely no

way the chlorinator can produce any chlorine if you

have no salt.

That's if you have a salt pool. If it is not salt

do exactly what waterbear has suggested.

Regards,

Michael Silvester

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Hi,

If you have a salt pool, there is absolutely no

way the chlorinator can produce any chlorine if you

have no salt.

That's if you have a salt pool. If it is not salt

do exactly what waterbear has suggested.

Regards,

Michael Silvester

If you read the first post they say that they have an automatic chlorinator turned all the way up (inline or offline chlorinator) with three STICK (of trichlor) also in the skimmer basket. There is no mention of a SWG. Also no salt reading was ever given but a TDS of 800 ppm was! Makes it pretty clear that this pool is on trichlor and NOT a SWG!

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Hi,

In my country, Automatic chlorinator could

mean anything.

You of all people should know that people

make up all sorts of names for equipment.

I know people that dont have a clue if their

pool is salt or not. So I dont think it was

such a crazy thing to say and that first

post could be taken either way.

Regards,

Michael Silvester

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