Non-chlorine Shock Made My Water Worse!

[KevinL]

I had a very weird chemical experience today and I can't make any sense of it. I would appreciate any help you guys can offer.

I tested by water at Leslie's at 11 o'clock this morning and they said my FC was 4.0, and CC was 4.53. Their computer recommended non-chlorine MPS shock, which I thought was a great idea because it's supposed to kill chloramines without raising the chlorine levels in the pool.

Anyway, I was dying of curiosity so I returned to Leslie's at 4:30 pm to get retested. Now, five hours later, my FC was 3.66, and CC was 4.74! I actually GAINED chloramines! And to make matters even crazier, their computer AGAIN recommended MORE non-chlorine shock.

So my question is, what was the point of doing a non-chlorine shock? And how is this result even possible?

My pool: ph=7.5, TA=88, Ca=201, CYA=40, TDS=1000

Thanks in advance, Kevin

 

[mgtfp]

MPS interferes with the CC test:

CC - Further Reading

www.troublefreepool.com

In a properly chlorinated outdoor pool following the recommended FC/CYA Levels, MPS is not recommended or required. FC with natural UV from the sun is sufficient to keep CC in check.

Trust your own testing with one of the recommended test kits (Test Kits Compared). Much more reliable than Leslie's, and you won't leave the shop with stuff you don't need, but less $$$ in your pocket. Test kit pays for itself in no time.

 

[proavia]

Pool Care Basics
Test Kits Compared

FC/CYA Levels

What does your water look like?

 

[jimbethesda]

So my question is, what was the point of doing a non-chlorine shock?

The only point is for the pool store to make money. As stated above, buy your own test kit (one of the recommended ones in the link above), and stay out of the pool store.

There is a small learning curve on this site, but once you get the hang of it, your pool will always sparkle, it will be safe to swim in, you’ll spend less time on it, and spend less money on it.

 

[KevinL]

Pool Care Basics
Test Kits Compared

FC/CYA Levels

What does your water look like?

Like a million bucks.

 

[KevinL]

MPS interferes with the CC test:

CC - Further Reading

www.troublefreepool.com

In a properly chlorinated outdoor pool following the recommended FC/CYA Levels, MPS is not recommended or required. FC with natural UV from the sun is sufficient to keep CC in check.

Trust your own testing with one of the recommended test kits (Test Kits Compared). Much more reliable than Leslie's, and you won't leave the shop with stuff you don't need, but less $$$ in your pocket. Test kit pays for itself in no time.

Thank you for your response. I also used one of the Taylor test kits, and it pretty much agreed with Leslie in reporting too much chlorine. But now I know why.

Maybe you can help me understand why my CC was too high this morning (FC 4.0, CC 4.53). It's weird because I did a Cal Hypo shock Tuesday evening (2 lbs Cal Hypo in my 20K gal pool) and therefore I would've expected much lower CC this morning. Any ideas where I might be going wrong?

 

[proavia]

In Long Beach CA, your fill water CH is probably quite high already. Adding CalHypo adds even more calcium - which you probably don't need.

Don't add any more non-chlorine shock. The MPS in that messes with the CC's.

What exact Taylor test kit are you using? They have a bunch of different ones.

 

[KevinL]

In Long Beach CA, your fill water CH is probably quite high already. Adding CalHypo adds even more calcium - which you probably don't need.

Don't add any more non-chlorine shock. The MPS in that messes with the CC's.

What exact Taylor test kit are you using? They have a bunch of different ones.

Thank you for the advice. My calcium hardness is 201. Are you advising me to just use the liquid chlorine as needed and skip this shock?
I'm using the Taylor K-1000 but have ordered the Taylor K-1004

 

[Bperry]

Thank you for the advice. My calcium hardness is 201. Are you advising me to just use the liquid chlorine as needed and skip this shock?
I'm using the Taylor K-1000 but have ordered the Taylor K-1004

You need the K2006C. That shock is just going to add more calcium so liquid is better.

Also, your chlorine isn’t too high. 7ppm is the max normal level you want to be at with CYA=40.

 

[mgtfp]

Thank you for your response. I also used one of the Taylor test kits, and it pretty much agreed with Leslie in reporting too much chlorine. But now I know why.

Maybe you can help me understand why my CC was too high this morning (FC 4.0, CC 4.53). It's weird because I did a Cal Hypo shock Tuesday evening (2 lbs Cal Hypo in my 20K gal pool) and therefore I would've expected much lower CC this morning. Any ideas where I might be going wrong?

Did you have a pool party, or lots of kids swimming in the pool? Most likely there was some bather "waste" that was still in the process of being oxidised by the chlorine you added.

Get started on reading through the Pool Care Basics. TFP does some things differently - I think the right way.

One of TFP's basic principles is acknowledging that CYA is on one hand crucial for residential outdoor pool maintenance, but that on the other hand the vast majority of what shows as "free" chlorine in the FC test is actually chlorine bound to CYA. It's protected from UV there, but doesn't have any sanitising effects anymore. But unfortunately it still shows up as FC in the test due to how the chemistry of the test works.

Therefore it's important to maintain FC in relation to the CYA level. Same ratios of FC/CYA yield same amounts of the actually sanitising and oxidising chlorine species (hypochlorous acid or HOCl). FC 6ppm with CYA 40ppm is in terms of HOCl for example equivalent to less than FC 0.15ppm with no CYA in the water.

All of this is reflected in the recommended FC/CYA Levels.

A pool maintained in the recommended target range doesn't need regular "shocking".

We have a SLAM Process, which stands for "Shock Level And Maintain", which gets applied to clear an algae infested pool. The important bit is that this is not a one-off shock dose, but maintaining elevated FC until the SLAM exit criteria are met. Another example: SLAM FC of 16ppm for CYA 40 ppm or FC 24ppm for CYA 60ppm are equivalent to FC 0.64 ppm with no CYA.

Any FC up to SLAM FC for the respective CYA level is safe to swim in. But I wouldn't set my foot in a public indoor pool that's maintained for example at FC 4ppm without CYA in the water, which is considered perfectly acceptable in most jurisdictions for commercial pools.

Crucial in all of this is knowing your levels. And we need to be able to trust your test results too, so we can give you advice. We don't have confidence to tell you "add this and that to your pool" based on pool store or test strip testing. But we do feel confident when test results are from one of the above recommended test kits.

 

[JamesW]

I tested by water at Leslie's at 11 o'clock this morning and they said my FC was 4.0, and CC was 4.53. Their computer recommended non-chlorine MPS shock, which I thought was a great idea because it's supposed to kill chloramines without raising the chlorine levels in the pool.

Anyway, I was dying of curiosity so I returned to Leslie's at 4:30 pm to get retested. Now, five hours later, my FC was 3.66, and CC was 4.74!

Those numbers are very unlikely.

Most likely, the TC (Total Chlorine) was 4.74, which makes the CC only (4.74 - 3.66) = 1.08.

In any case, the readings are unreliable and you probably don't have any significant CCs.

Get your own good test kit and check the FC and CC yourself.

Unless you have a lot of ammonia or used sulfamic acid, you are not going to have 4.74 ppm of CCs.

 

[JamesW]

So my question is, what was the point of doing a non-chlorine shock?

There is no point and all it does is waste your time and money and it can cause some interference in the FC and CC readings.

 

[JamesW]

Can you show the actual paperwork for the test results?

 

[JamesW]

As you can see, the reported numbers are Free Chlorine and Total Chlorine and not Combined Chlorine.

Their numbers are ridiculously specific to make them seem more accurate and credible.

You see the exact numbers and you think that they have to be accurate, right?

Wrong.

When the results have 18 digits to the right of the decimal point, you should probably question how they are getting such specific measurements.

At that point, you're counting individual molecules.

 

[KevinL]

As you can see, the reported numbers are Free Chlorine and Total Chlorine and not Combined Chlorine.

Their numbers are ridiculously specific to make them seem more accurate and credible.

You see the exact numbers and you think that they have to be accurate, right?

Wrong.

When the results have 18 digits to the right of the decimal point, you should probably question how they are getting such specific measurements.

At that point, you're counting individual molecules.

View attachment 504746

You are definitely correct. And I have noticed that certain of their test results tend to fluctuate from week to week even though they should not. Calcium hardness, for example.

 

[KevinL]

There is no point and all it does is waste your time and money and it can cause some interference in the FC and CC readings.

Thank you for this good advice. If I had known that MPS would mess up my CC measurements, I would've never added it.

 

[KevinL]

Did you have a pool party, or lots of kids swimming in the pool? Most likely there was some bather "waste" that was still in the process of being oxidised by the chlorine you added.

Get started on reading through the Pool Care Basics. TFP does some things differently - I think the right way.

One of TFP's basic principles is acknowledging that CYA is on one hand crucial for residential outdoor pool maintenance, but that on the other hand the vast majority of what shows as "free" chlorine in the FC test is actually chlorine bound to CYA. It's protected from UV there, but doesn't have any sanitising effects anymore. But unfortunately it still shows up as FC in the test due to how the chemistry of the test works.

Therefore it's important to maintain FC in relation to the CYA level. Same ratios of FC/CYA yield same amounts of the actually sanitising and oxidising chlorine species (hypochlorous acid or HOCl). FC 6ppm with CYA 40ppm is in terms of HOCl for example equivalent to less than FC 0.15ppm with no CYA in the water.

All of this is reflected in the recommended FC/CYA Levels.

A pool maintained in the recommended target range doesn't need regular "shocking".

We have a SLAM Process, which stands for "Shock Level And Maintain", which gets applied to clear an algae infested pool. The important bit is that this is not a one-off shock dose, but maintaining elevated FC until the SLAM exit criteria are met. Another example: SLAM FC of 16ppm for CYA 40 ppm or FC 24ppm for CYA 60ppm are equivalent to FC 0.64 ppm with no CYA.

Any FC up to SLAM FC for the respective CYA level is safe to swim in. But I wouldn't set my foot in a public indoor pool that's maintained for example at FC 4ppm without CYA in the water, which is considered perfectly acceptable in most jurisdictions for commercial pools.

Crucial in all of this is knowing your levels. And we need to be able to trust your test results too, so we can give you advice. We don't have confidence to tell you "add this and that to your pool" based on pool store or test strip testing. But we do feel confident when test results are from one of the above recommended test kits.

So much wisdom, wow. Thank you very much for taking the time to provide all this excellent information complete with examples. I have purchased the K2006 test kit and I'm going to stay away from nonchlorine shock. So you're saying that you would feel comfortable swimming in FC 16 ppm water?

 

[Newdude]

So you're saying that you would feel comfortable swimming in FC 16 ppm water?

The CYA sets the FC boundaries. Swimming is safe from minimum to SLAM at any CYA level. I can't count how many times I've swam in the high teens with a CYA of 70.

 

[mgtfp]

So you're saying that you would feel comfortable swimming in FC 16 ppm water?

Definitely. But it's important to know your CYA to know what's safe. And that goes both ways, not just on the high side, but also on the low side.

 

[wireform]

As you can see, the reported numbers are Free Chlorine and Total Chlorine and not Combined Chlorine.

Their numbers are ridiculously specific to make them seem more accurate and credible.

You see the exact numbers and you think that they have to be accurate, right?

Wrong.

When the results have 18 digits to the right of the decimal point, you should probably question how they are getting such specific measurements.

At that point, you're counting individual molecules.

View attachment 504746

Not that I give them an ounce of trust but the FC and TC are the same number which means you 4.47 FC and no CC's. Matter of fact I wouldn't trust the CYA of 95 either. Get your own kit and trust your own results.