Non-Chlorine Shock - SWG

[Cedarpool]

I find I have to add 1.5 pounds of non-chlorine shock about every three days to keep my FC up around 3-4. The FC slowly drifts down to about 1 at which time I add the shock and within about an hour the FC shoots back to 3-4. Then the process begins again, the FC falls over a few days, I shock and it quickly rockets back up. Any ideas as to what is causing this? I ran a total chlorine test with the FC at 1 and could not tell any difference in readings. Boosting the chlorine generator does not seem to help. I don't understand why the FC is falling and why non-chlorine shock is raising the FC so quickly and dramatically and hope that description fits a known problem and how to correct it. The cell is brand new and I assume is working since after shocking I get high FC readings.

My readings:

PH: 7.5
TA: 90
CH: 250
CYA: approx 65
Water Temp: 91
Salt: 4000 (this is the recommended level for my Jandy AquaPure Ei).

 

[duraleigh]

What is the non-chlorine shock?

 

[JohnT]

Welcome to TFP!

How are you testing for chlorine? Non-chlorine shock can fool some chlorine tests. Beyond that, it is expensive and not needed. Just use chlorine.

Many possibilities.

It could be that your generator isn't working. You can test for this by collecting a water sample at one of the pool returns and measuring the chlorine in that sample. If it is higher than the rest of the pool, it indicates you are generating chlorine.

It's also possible that you have something consuming chlorine faster than the generator can replace it. If that is the case, you need to follow the process in SLAMing Your Pool

It could be that your CYA level is lower than you think. The test is pretty subjective.

 

[Cedarpool]

Potassium Monopersulfate

 

[domct203]

Potassium Monopersulfate

I believe that will show up as CC, not FC.

Dom

- - - Updated - - -

I find I have to add 1.5 pounds of non-chlorine shock about every three days to keep my FC up around 3-4. The FC slowly drifts down to about 1 at which time I add the shock and within about an hour the FC shoots back to 3-4. Then the process begins again, the FC falls over a few days, I shock and it quickly rockets back up. Any ideas as to what is causing this? I ran a total chlorine test with the FC at 1 and could not tell any difference in readings. Boosting the chlorine generator does not seem to help. I don't understand why the FC is falling and why non-chlorine shock is raising the FC so quickly and dramatically and hope that description fits a known problem and how to correct it. The cell is brand new and I assume is working since after shocking I get high FC readings.

My readings:

PH: 7.5
TA: 90
CH: 250
CYA: approx 65
Water Temp: 91
Salt: 4000 (this is the recommended level for my Jandy AquaPure Ei).

What test kit are you using?

 

[Cedarpool]

Welcome to TFP!

How are you testing for chlorine? Non-chlorine shock can fool some chlorine tests. Beyond that, it is expensive and not needed. Just use chlorine.

Many possibilities.

It could be that your generator isn't working. You can test for this by collecting a water sample at one of the pool returns and measuring the chlorine in that sample. If it is higher than the rest of the pool, it indicates you are generating chlorine.

It's also possible that you have something consuming chlorine faster than the generator can replace it. If that is the case, you need to follow the process in SLAMing Your Pool

It could be that your CYA level is lower than you think. The test is pretty subjective.

Testing with a Taylor DPD kit (using reagents R-0001 & R-0002). I have a waterfall that comes straight from the pump so I check the generator operation there (no issue with dilution by the pool water around a jet) and it is making chlorine. Also, since I am not manually adding any chlorine (just the the non-chlorine shock), am not getting algae blooms and see FC readings I assume that is working properly. Is it possible something is using up that much chlorine (assuming the FC test is accurate) without any visible indications of a problem?

Regarding the CYA, I bought a 50ppm standarized solution to train myself so I think 65 is pretty close.

 

[domct203]

I'm thinking the MPS is oxidizing organics allowing the FC from the SWG to remain unused (and register on a test), until the MPS dissipates at which point the FC is rapidly consumed by said organics.

I'm in agreement that you start using bleach (liquid chlorine) to supplement your SWG.

Dom

 

[JohnT]

Testing with a Taylor DPD kit (using reagents R-0001 & R-0002). I have a waterfall that comes straight from the pump so I check the generator operation there (no issue with dilution by the pool water around a jet) and it is making chlorine. Also, since I am not manually adding any chlorine (just the the non-chlorine shock), am not getting algae blooms and see FC readings I assume that is working properly. Is it possible something is using up that much chlorine (assuming the FC test is accurate) without any visible indications of a problem?

Regarding the CYA, I bought a 50ppm standarized solution to train myself so I think 65 is pretty close.

Seems like the most likely scenario is that you have excess chlorine consumption. You can get in a mode where you have barely enough chlorine to keep the algae under control. I would probably shut the SWCG off and follow the SLAM process. Once you can pass the Overnight Chlorine Loss Test you can turn the SWCG back on and see if it can keep up.

 

[Cedarpool]

Seems like the most likely scenario is that you have excess chlorine consumption. You can get in a mode where you have barely enough chlorine to keep the algae under control. I would probably shut the SWCG off and follow the SLAM process. Once you can pass the Overnight Chlorine Loss Test you can turn the SWCG back on and see if it can keep up.

At my CYA a SLAM will require very high FC levels (26). Will an FAS-DPD kit read that high (need to order one) and what is a safe level to allow swimming again? My family uses the pool daily so if it would take a while for swimming maybe I will maintain with additional chlorine and SLAM later in the year to hopefully solve the problem. Thanks for the guidance!

 

[JohnT]

At my CYA a SLAM will require very high FC levels (26). Will an FAS-DPD kit read that high (need to order one) and what is a safe level to allow swimming again? My family uses the pool daily so if it would take a while for swimming maybe I will maintain with additional chlorine and SLAM later in the year to hopefully solve the problem. Thanks for the guidance!

The FAS-DPD test will read up to 50ppm. Swimming at SLAM levels is safer than swimming at 0ppm FC.

 

[chem geek]

Yes, a FAS-DPD will read to 50 ppm FC and is why we recommend you get a TFTestkits TF-100 or a Taylor K-2006 (see Test Kits Compared). If you already have a Taylor K-2005, then you can just add the FAS-DPD chlorine test to it.

You should not be using non-chlorine shock in your outdoor residential pool exposed to sunlight. It will not do anything chlorine and sunlight won't do. MPS will register as CC in the DPD chlorine test unless the MPS level is very high in which case it can bleed through into the FC test. For the FAS-DPD test, if there is any chlorine in the water at all, then the MPS will show up as FC in that test. You can either wait until the MPS gets used up or if you insist on using MPS then I suggest you get the Taylor K-2042 MPS interference remover.

 

[Ncdamsel]

What is the non-chlorine shock?

I was gonna ask the same thing[emoji51]


Sent from my iPhone using Tapatalk

 

[Cedarpool]

Yes, a FAS-DPD will read to 50 ppm FC and is why we recommend you get a TFTestkits TF-100 or a Taylor K-2006 (see Test Kits Compared). If you already have a Taylor K-2005, then you can just add the FAS-DPD chlorine test to it.

You should not be using non-chlorine shock in your outdoor residential pool exposed to sunlight. It will not do anything chlorine and sunlight won't do. MPS will register as CC in the DPD chlorine test unless the MPS level is very high in which case it can bleed through into the FC test. For the FAS-DPD test, if there is any chlorine in the water at all, then the MPS will show up as FC in that test. You can either wait until the MPS gets used up or if you insist on using MPS then I suggest you get the Taylor K-2042 MPS interference remover.

Is the MPS not effective/waste of money or is it more an issue of it potentially corrupting the FC test? I had read (not on this site) that MPS is the preferred shock for SWCG pools so that is why I have been using it (and have quite a bit left!). I am certainly not disputing your guidance, just really interested in learning all there is to know about my pool and it's maintenance (new pool owner as of January). Do you think I am bleeding into the FC test (using the label dose of 1 1/2 pounds for my 15,000 gallons) or like Dom suspected is it oxidizing the organics and freeing up the FC (and therefore the FC reading is accurate)? Also is there an upper safety limit for FC after shocking or is the shock FC for a given CYA always safe for swimming? Don't want the kids jumping into unsafe water, either due to 0 FC or FC that is too high.

Thinking a first step is to order K-2006 and conduct an overnight loss test to confirm that is what is happening to my FC (as opposed to loss due to sun or swimming)?

Thanks!

 

[chem geek]

What you read is wrong. First of all, if you properly maintain the FC/CYA ratio you should not need to shock your pool, period. Second, if you do need to SLAM - Shock Level and Maintain your pool because you were lax and let the FC/CYA level get too low such that algae started to grow or you had an unusual one-time event, you would do so with chlorine, not MPS. MPS can be useful in indoor pools that have chloramine issues, though the use of UV or ozone systems are also effective in that situation. For outdoor residential pools exposed to sunlight, there is no need for supplemental oxidation systems be it ozone, UV, MPS or anything else. This is because the UV in sunlight breaks down chlorine into hydroxyl radicals that are very short-lived but powerful oxidzers that help break down chemicals that chlorine is otherwise slow to oxidize. Also, the bather load in most residential pools is exceptionally low. One person-hour in your 15,000 gallon pool only requires 0.07 ppm FC to oxidize the bather waste.

Also, MPS does not even oxidize chemicals that chlorine deals with such as ammonia and inorganic chloramines (see this post). MPS does oxidize some chemicals that chlorine doesn't, but they aren't the typical chemicals found in bather load. The ones found in bather load are either oxidized by chlorine or by both chlorine and MPS.

Where did you read the information that told you that MPS is the preferred shock for SWCG pools?

As for the SLAM FC level for the CYA level, it is equivalent to an FC of 0.6 ppm FC with no CYA so while 10 times higher than the minimum FC/CYA level needed to prevent green and black algae growth using chlorine alone, it is lower than found in commercial/public pools. You may notice a chlorine smell and your swimsuits, skin, and hair will get oxidized 10 times faster so that a day of swimming is similar to 10 days at the minimum FC/CYA level, but it is not unsafe.