Correlation of Chlorine with MPS (Non-Chlorine Shock)

[SpaWife]

In an effort to keep the water from smelling like sweat, and to confront a pesky .5 CC, I decided to shock with non-chlorine shock/oxidizer weekly. (I know this will raise my CYA, and I'll navigate that as I go.)

I'm curious about what happened to the chlorine level when I shocked it this time (2nd time since purge/drain/refill on 12-16).

I didn't test before soaking, because I knew the chlorine level was good.

After a 1 hour 2 person soak on 1-8, I tested:
5 FC, .5 CC
7.9 pH
40 CYA
101°

I didn't have time after that soak & test to address the tub, because I went out of the house for a bit. I came back to it 2+ hours later and did the Oxidizer/Non-Chlorine Shock. 20 minutes after that, I re-tested:
7 FC, .5 CC
7.8 pH
60 Alkalinity

I was intrigued that the FC increased! Can you explain to me how that happened? Had the chlorine been hiding as something other than FC/CC, and then converted back to FC?

The next day (today, 1-9) I tested it a little over 24 hours later:
1.5 FC, 0 CC
7.8 pH

[I know I let it get too low (1.5 FC). I meant to intervene sooner. So I added 1/3 cup bleach 10%.]

I'm impressed that it got back to 0 CC! That .5 CC had been lingering since 12-29, despite shocking it on 12-30. So maybe the shock helps with the lingering CC?

I've been letting the spa breathe a bit lately (an hour on the 8th, an hour on the 5th, 3 hours on the 4th). Also, I always keep the cover open for 30 min when I've added shock or chlorine.

I'd love your feedback on my shock (Oxidizer/Non-Chlorine Bleach/MPS) experiment. Why/How did it raise my FC level? Does it help get rid of CC? Does "breathing" help eliminate CC?

P.S. Last time (before this recent purge/drain/refill) I had done the weekly SLAM that is recommended in the Chlorine info sticky. But you told me that's no longer recommended. So this time around I figured I'd experiment with Non-Chlorine Shock.

 

[Bperry]

In an effort to keep the water from smelling like sweat, and to confront a pesky .5 CC, I decided to shock with non-chlorine shock/oxidizer weekly. (I know this will raise my CYA, and I'll navigate that as I go.)

I'm curious about what happened to the chlorine level when I shocked it this time (2nd time since purge/drain/refill on 12-16).

I didn't test before soaking, because I knew the chlorine level was good.

After a 1 hour 2 person soak on 1-8, I tested:
5 FC, .5 CC
7.9 pH
40 CYA
101°

I didn't have time after that soak & test to address the tub, because I went out of the house for a bit. I came back to it 2+ hours later and did the Oxidizer/Non-Chlorine Shock. 20 minutes after that, I re-tested:
7 FC, .5 CC
7.8 pH
60 Alkalinity

I was intrigued that the FC increased! Can you explain to me how that happened? Had the chlorine been hiding as something other than FC/CC, and then converted back to FC?

The next day (today, 1-9) I tested it a little over 24 hours later:
1.5 FC, 0 CC
7.8 pH

[I know I let it get too low (1.5 FC). I meant to intervene sooner. So I added 1/3 cup bleach 10%.]

I'm impressed that it got back to 0 CC! That .5 CC had been lingering since 12-29, despite shocking it on 12-30. So maybe the shock helps with the lingering CC?

I've been letting the spa breathe a bit lately (an hour on the 8th, an hour on the 5th, 3 hours on the 4th). Also, I always keep the cover open for 30 min when I've added shock or chlorine.

I'd love your feedback on my shock (Oxidizer/Non-Chlorine Bleach/MPS) experiment. Why/How did it raise my FC level? Does it help get rid of CC? Does "breathing" help eliminate CC?

P.S. Last time (before this recent purge/drain/refill) I had done the weekly SLAM that is recommended in the Chlorine info sticky. But you told me that's no longer recommended. So this time around I figured I'd experiment with Non-Chlorine Shock.

Using MPS messes with the FC/CC test. Likely the reason for the weirdness. 0.5CC is within the error tolerance of the test so I wouldn’t be trying to mess with it. You can help get rid of CC by just opening up the cover for a bit during the day.

 

[JoyfulNoise]

MPS (oxidizer/non-chlorine shock) remains in the water for quite some time. The main problem with testing is that it doesn’t turn the chlorine indicator dye pink but it does use up extra drops of the R-0871 titrant. So it appears that you have higher FC because you have to add more drops to get the pink dye to turn clear but in reality it is simply the excess MPS that’s reacting with the titrant. So, no, there wasn’t any “hidden” FC anywhere.

 

[Mdragger88]

In an effort to keep the water from smelling like sweat, and to confront a pesky .5 CC, I decided to shock with non-chlorine shock/oxidizer weekly. (I know this will raise my CYA, and I'll navigate that as I go.)

Mps doesn’t contain cya.
It will however read as cc’s on the test without using the special interference reagent.

I'm curious about what happened to the chlorine level when I shocked it this time (2nd time since purge/drain/refill on 12-16).

I didn't test before soaking, because I knew the chlorine level was good.

After a 1 hour 2 person soak on 1-8, I tested:
5 FC, .5 CC
7.9 pH
40 CYA
101°

I didn't have time after that soak & test to address the tub, because I went out of the house for a bit. I came back to it 2+ hours later and did the Oxidizer/Non-Chlorine Shock. 20 minutes after that, I re-tested:
7 FC, .5 CC
7.8 pH
60 Alkalinity

I was intrigued that the FC increased! Can you explain to me how that happened? Had the chlorine been hiding as something other than FC/CC, and then converted back to FC?

The next day (today, 1-9) I tested it a little over 24 hours later:
1.5 FC, 0 CC
7.8 pH

[I know I let it get too low (1.5 FC). I meant to intervene sooner. So I added 1/3 cup bleach 10%.]

I'm impressed that it got back to 0 CC! That .5 CC had been lingering since 12-29, despite shocking it on 12-30. So maybe the shock helps with the lingering CC?

Either mps or chlorine can accomplish this. You don’t necessarily even need to raise fc to slam level to help eliminate cc’s - sometimes just raising to around 10ppm can be enough with a cya of 30-40. This can also help you get through to your next soak without having to micro dose the tub all the time.

I've been letting the spa breathe a bit lately (an hour on the 8th, an hour on the 5th, 3 hours on the 4th). Also, I always keep the cover open for 30 min when I've added shock or chlorine.

That is good continue to do so!

I'd love your feedback on my shock (Oxidizer/Non-Chlorine Bleach/MPS) experiment. Why/How did it raise my FC level?

It likely just interfered with the reagent causing you to use more drops resulting in a higher fc number- this has been reported when large amounts of mps were used. Generally it mostly interferes with the cc reagent.

Does it help get rid of CC?

It can - sorta, but so does chlorine in adequate amounts. Chlorine is both a sanitizer & an oxidizer. Much simpler to just use chlorine.
Mps also adds sulfates which are not good for your heater.

Btw 0.5 ppm of cc’s is perfectly acceptable.

Does "breathing" help eliminate CC?

Yes

P.S. Last time (before this recent purge/drain/refill) I had done the weekly SLAM that is recommended in the Chlorine info sticky. But you told me that's no longer recommended. So this time around I figured I'd experiment with Non-Chlorine Shock.

Not necessarily no longer recommended persay.
It’s perfectly fine to do just a bit unnecessary if adequate fc is always maintained. (Fc is not allowed to fall below minimum for the cya level FC/CYA Levels)
Why add things for no reason?

 

[phonedave]

And, just to chime in with my PSA on MPS.

Some people have allergic reactions to MPS (maybe). As far as I know it has not been 100% proven to be an issue, but it might be an issue and cause a rash in some people.

But, given:

MPS can throw off your FAS/DPD test
Chlorine does the same thing as MPS (oxidized CCs)
MPS may cause a rash.

I say, no need to go using MPS

 

[JoyfulNoise]

Where MPS can sometimes be useful is when hot tubs are infrequently used. Let’s say you’re just a busy person and the best you manage is a quick soak on Wednesday night and then maybe a longer soak on Sat evening. Or you know that there’s probably zero chance you’re going to get into the tub for the next 7-10 days or so. In that circumstance, MPS can be used to maintain a high oxidation level that retards biological growth but allows you to not worry as much about keeping the FC level up. MPS lasts a lot longer than chlorine at higher tub temperatures. So if you have one of those long spells between uses you can dose the chlorine to your preferred FC level, add MPS to help destroy organic better and then maybe add another dose of MPS midway. Then, before you use the tub again, test and add enough chlorine to factor in the person-hours you expect and then dose again after you’re done. It’s one way of not constantly having to attend to a hot tub but it is critical to dose chlorine before use so that you are assured pathogens will be neutralized.

Obviously if you have a Saltron-type drape over SWG that can keep adding chlorine during long breaks and maintain that small residual FC, then that’s great. But not everyone has or wants to use an SWG and so the MPS doses is what bridges the long gaps while not in use.