FAS DPD and OTO chlorine rise after non-chlorine shock

[jmcmd1980]

Last weekend, I had a heavy bather load so I used 2 bags of Leslie's Fresh N Clear non-chlorine shock. I have a SWG, pool installer set to 85% and left it at that when they abandoned me. My pool is about 5-6 weeks post fill.

Today on testing, Free and combined chlorine by FAS-DPD is 9.2, had been running just under 5 prior. I did the simple OTO test also and sample turned dark yellow.

Is this an artifact of the oxidizer in the Fresh N Clear. I found one forum entry alluding to this. Do I need to do anything about this? Reduce SWG or leave it alone and let chlorine return to normal levels?

Thanks as always, Jim

 

[mknauss]

MPS shows as CC in the water for some time.

It will go away over time. Just use your FC levels.

Also -- please do not use that product again. It adds sulfates to your pool water and slowly destroys your SWCG.

 

[jmcmd1980]

I should have researched it more before just throwing it in the pool. Hopefully it will not take long to dissipate. I assume I do not need to adjust my SWG.

Jim

 

[mknauss]

I assume I do not need to adjust my SWG.

I would not. Test FC every few days and see how it settles.

 

[Newdude]

Also switch to 10ml samples. Each drop is 1/2 FC. Plenty close enough for what we need. For example, your 9.X is GREAT and a 2.X would suck. It'll save 2.5 times the drops.

 

[jmcmd1980]

I would not. Test FC every few days and see how it settles.

Thanks again, one more question, if you don’t mind. If the pool had a lot of organic contaminants as it’s a new pool, is it possible that the oxidizer destroyed those and made the free chlorine level go up? After I did the total and free chlorine test, I put in the reagent to look for combined chlorine, and it was only .2, one drop. Or am I interpreting this wrong?

 

[mknauss]

Using the FAS-DPD, the first test, scoop of R0870 powder in 10ml of water followed by R0871 drops to clear, is the FC test. Then you add 5 drops of R0003 and then use the R0871 again to clear, that is the CC test. Each drop is 0.5 ppm.
TC is meaningless.

The MPS will not show up as FC. Only CC.

 

[jmcmd1980]

Also switch to 10ml samples. Each drop is 1/2 FC. Plenty close enough for what we need. For example, your 9.X is GREAT and a 2.X would suck. It'll save 2.5 times the drops.

Thanks, I will switch to the smaller sample size. I still don’t know why my free chlorine was so high after using the oxidizer, as I noted. I did the test for combined chlorine, and it was only one drop or .2 with the test sample I used.

 

[mknauss]

I still don’t know why my free chlorine was so high

What is your SWCG creating each day in FC? Need hours run, % generation, and SWCG type and use Poolmath.

 

[jmcmd1980]

What is your SWCG creating each day in FC? Need hours run, % generation, and SWCG type and use Poolmath.

I run at 3750 RPM 9 AM to 6 PM, 85%, Jandy PLC 1400 cell. I’ll put it in Pool Math.

 

[jmcmd1980]

Sorry, 2750 RPM, not 3750

 

[mknauss]

You are creating 3.4 ppm FC each day. I would think that is about right in your area. Is the pool in a screened enclosure? There is less FC loss to UV if screened in.

Not sure why you would be running the pump at such a high rpm. Try 1200 rpm and see if the SWCG is happy and the pool gets skimmed.

 

[jmcmd1980]

The pool is fenced, but not screened. We have a champagne spa and a sun deck, so the spa likely requires some extra RPMs to push the water over the top edge and cascade down.

 

[mknauss]

Do you have automation with the spa? It is not shown on your signature.

 

[DrewLG]

If the pool had a lot of organic contaminants as it’s a new pool, is it possible that the oxidizer destroyed those and made the free chlorine level go up? After I did the total and free chlorine test, I put in the reagent to look for combined chlorine, and it was only .2, one drop. Or am I interpreting this wrong?

Yes, you're interpreting it wrong.

The important thing to know is that KMPS reacts with R-0871 and also with R-0003. When people say that KMPS only interferes with the CC measurement, they're talking about the color-matching DPD test, not the FAS-DPD titration ("drop") test.

In the DPD test, you first measure FC by adding reagents and comparing colors -- this part isn't affected by KMPS -- and then you measure total chlorine by adding R-0003 to the solution and comparing colors again. KMPS in the water will react with the R-0003, producing a falsely high measurement of total chorine. Since total chlorine is FC + CC, and the FC measurement was accurate, CC falsely appears higher than it really is.

In the FAS-DPD drop test, KMPS reacts with the R-0871 FAS drops, so in that test it's the FC measurement that is falsely high. By the time R-0003 is added to the solution to measure CC, all of the KMPS has already reacted, leaving none to affect the CC measurement. So in the FAS-DPD test, KMPS affects the FC measurement but not the CC measurement.

KMPS will dissipate in a few days. But if you anticipate that you'll be using KMPS regularly, you may want to purchase Taylor's K-2042 kit, which eliminates KMPS interference from the chlorine tests. A link to the kit is in my signature.

 

[wireform]

I run at 3750 RPM 9 AM to 6 PM, 85%, Jandy PLC 1400 cell. I’ll put it in Pool Math.

That comes out to 3.4ppm

 

[jmcmd1980]

Do you have automation with the spa? It is not shown on your signature.

I have the iAquaLink app and can turn the spa on and off, blower, and heat

 

[mknauss]

So you have Aqualink automation. If you wish to reduce the time the spa spillover runs and reduce the rate the pH rises, we can guide you on how to do that.

 

[jmcmd1980]

Yes, you're interpreting it wrong.

The important thing to know is that KMPS reacts with R-0871 and also with R-0003. When people say that KMPS only interferes with the CC measurement, they're talking about the color-matching DPD test, not the FAS-DPD titration ("drop") test.

In the DPD test, you first measure FC by adding reagents and comparing colors -- this part isn't affected by KMPS -- and then you measure total chlorine by adding R-0003 to the solution and comparing colors again. KMPS in the water will react with the R-0003, producing a falsely high measurement of total chorine. Since total chlorine is FC + CC, and the FC measurement was accurate, CC falsely appears higher than it really is.

In the FAS-DPD drop test, KMPS reacts with the R-0871 FAS drops, so in that test it's the FC measurement that is falsely high. By the time R-0003 is added to the solution to measure CC, all of the KMPS has already reacted, leaving none to affect the CC measurement. So in the FAS-DPD test, KMPS affects the FC measurement but not the CC measurement.

KMPS will dissipate in a few days. But if you anticipate that you'll be using KMPS regularly, you may want to purchase Taylor's K-2042 kit, which eliminates KMPS interference from the chlorine tests. A link to the kit is in my signature.

Thanks for the explanation, makes perfect sense. Jim

 

[jmcmd1980]

So you have Aqualink automation. If you wish to reduce the time the spa spillover runs and reduce the rate the pH rises, we can guide you on how to do that.

Yes, I would be interested in knowing how to do that