Increasing Free Chlorine in Covered Pool in absence of CYA

[mikeyliny]

If a pool is covered and both TC and FC are zero, what would prevent chlorine from being increased after chlorine is added?

There are many posts here that suggest increasing CYA in "chlorine lock."

My understanding, however, is that CYA will prevent chlorine degradation from taking place.

2Cl- + 2H2O + sunlight → Cl2 + 2OH- + H2

Testing

I have different testing units including
1. Taylor K-2006C
2. EasyTest Test Strips
3. HACH Acquacheck Test Strips

My practical case
After adding about 2 Gallons of Sodium Hypochlorite Solution to 17,500 gallons of water, I tested my pool (using strips and also Taylor) and TC + FC levels that are zero, pH is around 7.4. CYA=0, but hte pool is covered.

I then, used my salt water generator at superchlorinate after adding salt (and testing showed level of 3900), after leaving this on superchlorinate for 24 hours the salt level registered 3700, but again FC/TC are zero.

Since the pool is covered with an autocover, so I think that this should obviate CYA playing a factor. Though the tested level is close to zero. I don't believe this should be a factor in this case.

Experiment
I added about 1 drop of the sodium hypochlorite solution to 1 cup of pool water, and using a test strip the FC registered at the highest level of the test 20 (very high).

Pending
I just added another 2 gallons of chlorine, and plan to add CYA.

Meanwhile, what else could account for FC levels not rising, if the TC=FC and the pool is covered?

PS the water is clear, pump is running, filter pressure seems normal

 

[wireform]

Firstly how are you testing? Can you please update your signature with the link below in my signature.
It doesn't matter covered or not but 30ppm minimum is need to keep anyone swimming safe. 1 ppm fc is more harsh without cya then 10 fc with 30 ppm cya. The SWCG is there to maintain the chlorine and will not take the place of LC to bring it up to level. You may also have AMMONIA in the water and that can eat all the chlorine and cya until it's eliminated. You would need to keep pouring in LC until the water maintains 10 ppm for 15 minutes and then get the CYA into the water via the sock method.

 

[Donldson]

If you are using test strips, the first suspect is always testing error.

Also, no posts here ever suggest anything is related to "chlorine lock" as it is a made up term for pool stores to throw out when they are stumped.

 

[mikeyliny]

Firstly how are you testing? Can you please update your signature with the link below in my signature.
It doesn't matter covered or not but 30ppm minimum is need to keep anyone swimming safe. 1 ppm fc is more harsh without cya then 10 fc with 30 ppm cya. The SWCG is there to maintain the chlorine and will not take the place of LC to bring it up to level. You may also have AMMONIA in the water and that can eat all the chlorine and cya until it's eliminated. You would need to keep pouring in LC until the water maintains 10 ppm for 15 minutes and then get the CYA into the water via the sock method.

Testing

I have verified my measurments using different testing units including
1. Taylor K-2006C
2. EasyTest Test Strips
3. HACH Acquacheck Test Strips

In the past, I have found that the test-strips have been relatively accurate, never varied significantly from Taylor-2006C results for Chlorine, but I use it to cross-validate results anyways or when I am having difficulty balancing such as in this as I believe the Taylor-2006C is the gold-standard for reliability.

 

[JJ_Tex]

Meanwhile, what else could account for FC levels not rising, if the TC=FC and the pool is covered?

PS the water is clear, pump is running, filter pressure seems normal

Any algae can consume FC, even if the algae is not to the point to cause cloudiness or be otherwise visible. This is very likely if your chlorine has been at zero.

As Donldson said, test strips are not precise at all and not recommended. Also "chlorine lock" is a pool store term. Here at TPF we treat FC as a variable based upon your CYA. The higher your CYA the higher your FC should be to properly sanitize. That is way too complex of a concept for pool stores, so they keep everything static and then makeup terms like "chlorine lock", "your water is old", etc. when they cannot explain why their FC of 1-3 recommendation isn't working.

 

[mikeyliny]

Firstly how are you testing? Can you please update your signature with the link below in my signature.
It doesn't matter covered or not but 30ppm minimum is need to keep anyone swimming safe. 1 ppm fc is more harsh without cya then 10 fc with 30 ppm cya. The SWCG is there to maintain the chlorine and will not take the place of LC to bring it up to level. You may also have AMMONIA in the water and that can eat all the chlorine and cya until it's eliminated. You would need to keep pouring in LC until the water maintains 10 ppm for 15 minutes and then get the CYA into the water via the sock method.

Testing

I have verified my measurments using different testing units including
1. Taylor K-2006C
2. EasyTest Test Strips
3. HACH Acquacheck Test Strips

In the past, I have found that the test-strips have been relatively accurate, never varied significantly from Taylor-2006C results for Chlorine, but I use it to cross-validate results anyways or when I am having difficulty balancing such as in this as I believe the Taylor-2006C is the gold-standard for reliability.

If you are using test strips, the first suspect is always testing error.

Also, no posts here ever suggest anything is related to "chlorine lock" as it is a made up term for pool stores to throw out when they are stumped.

I didn't realize it was a made up term--that is good to know in quotations. Still, I find the term "chlorine lock" useful to communicate this situation as concisely as possible.

 

[mikeyliny]

Any algae can consume FC, even if the algae is not to the point to cause cloudiness or be otherwise visible. This is very likely if your chlorine has been at zero.

As Donldson said, test strips are not precise at all and not recommended. Also "chlorine lock" is a pool store term. Here at TPF we treat FC as a variable based upon your CYA. The higher your CYA the higher your FC should be to properly sanitize. That is way too complex of a concept for pool stores, so they keep everything static and then makeup terms like "chlorine lock", "your water is old", etc. when they cannot explain why their FC of 1-3 recommendation isn't working.

If there is algae in the pool would TC=FC? My undersanding is that the Total Chlorine would register higher if anything is consuming Chlorine. As mentioned I have both Taylor K2006C and Test Strips. Third, and this is part of my main question, CYA should probably not be relevant when the pool is covered.

 

[mknauss]

If there is algae in the pool would TC=FC?

Yes.

CYA should probably not be relevant when the pool is covered.

If 100%. No UV whatsoever.

 

[Newdude]

If there is algae in the pool would TC=FC?

If your FC is 0, then yes.

5 TC
-2 CC
=3 FC

0 TC
=0 CC/FC (once the cover has been open for a minute or two)

 

[mikeyliny]

My pool Chlorine isnt rising after adding 2 Gallons of Sodium Hypochlorite solution.

Taylor K-2006C testing shows that
FC=0
TC=0
pH=7.4
CYA=0, but my pool is covered.

Please correct me if my assumptions are incorrect:
1. CYA prevents chlorine degradation from taking place: 2Cl- + 2H2O + sunlight → Cl2 + 2OH- + H2, therefore, if my pool is covered, which it is, it should not be a factor in why my chlorine levels arent rising
2. When algae or other elements are consuming additional chlorine then TC>FC and additional chlorine should increase the levels of TC, while not affecting the FC until whatever is consuming the Chlorine can no longer do that. Therefore, in my pool that could not be the case since addition of chlorine did not increase TC and both FC&TC are equal to zero

This leaves me a bit stumped. I'm not sure why Chlorine is not rising. One idea I had is that there is something that is consuming chlorine that is trapped in my filter (perhaps dead blood worms or some other organism). Since I am testing the water in the pool, the Total Chlorine is still zero (since that is not the residence of these organisms). If this is the case, adding more chlorine would eventually increase levels, but I would prefer not to have to clean out the filters if I don't have to do that.

Anyways my next steps will be:
1. Adding another 2 Gallons of sodium hypochlorite & testing
2. Adding CYA (which will arrive on Tuesday & then the adding sodium hypochlorite and then testing
3. Cleaning out the filter & then sodium hypochlorite & testing

What do you think?

 

[mikeyliny]

If your FC is 0, then yes.

5 TC
-2 CC
=3 FC

0 TC
=0 CC/FC (once the cover has been open for a minute or two)

Can you please elaborate, I'm not sure I fully undestand your answer.

 

[mikeyliny]

If there is algae in the pool would TC=FC?

Yes

Let me rephrase, if there is algae in the pool is it possible that TC=0 and FC=0 after adding 2 gallons of chlorine?

in this case, if FC stays at 0, then TC should rise in the form of CC, assuming there is algae or something else consuming chlorine

 

[Newdude]

Can you please elaborate, I'm not sure I fully undestand your answer.

Thanks. It proves even further how TC is a junk parameter.

The components of the equation (TC and CC) are important. The answer (TC) doesn't tell you much. It could be 3+2 = 5, or 5+0= 5, with 2 totally different outcomes here.

But with 0 FC, there likely won't be any CCs either.

Let me rephrase, if there is algae in the pool is it possible that TC=0 and FC=0 after adding 2 gallons of chlorine?

It depends how much time has passed. An hour or two later, you should see some CCs and less FC. Several hours later there can be 0 FC and the CCs already burned off.

When you open the cover, if there is FC left and algae, it will continue to create CCs and you will be able to test the CCs. If the FC is long gone, no new CCs are being produced and the existing CCs will burn off in the time it takes to open the cover, leaving you with 0 FC and 0 TC.

 

[Bperry]

Please correct me if my assumptions are incorrect:
1. CYA prevents chlorine degradation from taking place: 2Cl- + 2H2O + sunlight → Cl2 + 2OH- + H2, therefore, if my pool is covered, which it is, it should not be a factor in why my chlorine levels arent risin

It does not prevent chlorine degradation. It only slows down degradation caused by sunlight, but also sunlight isn’t the only cause of degradation.

Liquid chlorine in the bottle will degrade all by itself over time.

 

[mikeyliny]

Here is where I'm at. After adding another 2 gallons of sodium hypochlorite solution, and testing after 30 minutes, I'm registering some chlorine finally
FC=2
TC=2 (so CC=0)

Given the amount of chlorine I have had to add in order to register a reading, 4 gallons, nearly twice the suggested amount to "shock" a 17,500 gallon pool, something had to be absorbing/consuming the chlorine I was adding.

The fact that the prior tests were not showing any chlorine, must mean that whatever was consuming the chlorine was trapped in the filter.

In other words, in theory, if opened up the filter, and tested the water from inside the filter, it should have been showing high levels of total chlorine, mostly in the form of combined chlorine.

Is there any other viable explanation?

 

[Bperry]

Here is where I'm at. After adding another 2 gallons of sodium hypochlorite solution, and testing after 30 minutes, I'm registering some chlorine finally
FC=2
TC=2 (so CC=0)

Given the amount of chlorine I have had to add in order to register a reading, 4 gallons, nearly twice the suggested amount to "shock" a 17,500 gallon pool, something had to be absorbing/consuming the chlorine I was adding.

The fact that the prior tests were not showing any chlorine, must mean that whatever was consuming the chlorine was trapped in the filter.

In other words, in theory, if opened up the filter, and tested the water from inside the filter, it should have been showing high levels of total chlorine, mostly in the form of combined chlorine.

Is there any other viable explanation?

Without CYA, chlorine will degrade very quickly, even with a cover on. Add some algae and the chlorine will be used up even quicker.

 

[kimkats]

chlorine lock

Most of the time when a person talks about "chlorine lock" it is when the CYA is way high and they are having a hard time putting in enough chlorine to keep the pool clear in the long run. Most CYA tests only go to 100 (including the Taylor kit) so the CYA could be much higher.

If you are worried about what is in the filter then you need to take it apart and clean it. Me? I don't think that is is as the chlorinated water is flowing through the filter when the pump it on.

What I think was happening is you may have had ammonia in the water. That would explain why you have 0 CYA as every once in awhile it will form ammonia. It can take a LOT of chlorine to get rid of the ammonia. One way to "test" for it is to add a set amount of chlorine to the pool and test for FC within 10 mins of adding the chlorine. Using pool math see how much the chlorine you added should have raised the FC. If it is lower than pool says it should be by quite a bit then you know you are in a battle with the ammonia . Keep adding chlorine over and over and over again until you start holding FC.

 

[jimbethesda]

Here is where I'm at. After adding another 2 gallons of sodium hypochlorite solution, and testing after 30 minutes, I'm registering some chlorine finally
FC=2
TC=2 (so CC=0)

Given the amount of chlorine I have had to add in order to register a reading, 4 gallons, nearly twice the suggested amount to "shock" a 17,500 gallon pool, something had to be absorbing/consuming the chlorine I was adding.

The fact that the prior tests were not showing any chlorine, must mean that whatever was consuming the chlorine was trapped in the filter.

In other words, in theory, if opened up the filter, and tested the water from inside the filter, it should have been showing high levels of total chlorine, mostly in the form of combined chlorine.

Is there any other viable explanation?

Bad/expired chlorine?

 

[Newdude]

The fact that the prior tests were not showing any chlorine, must mean that whatever was consuming the chlorine was trapped in the filter.

In other words, in theory, if opened up the filter, and tested the water from inside the filter, it should have been showing high levels of total chlorine, mostly in the form of combined chlorine.

This is pool store talk for when they can't explain it and just make up something ridiculous.

If they did not directly tell you this, you overheard them telling the person in front of you at some point and it wasn't 'your' idea a month or two later when it popped into your head.

 

[mikeyliny]

Bad/expired chlorine?

possible. I'm working one by one to eliminate possible weak points starting with the easiest/least work first: Chorinator, chlorine, filtration. But i was not using my chlorinator because I thought maybe it wasnt working. I added about a drop of the chlorine to a cup of pool water and tested the cup with a strip which showed very high chlorine concentration. I think it is possible.