MPS and Free Chlorine using Taylor R-0867 Deox Reagent

[contentedPilgrim]

I've been tracking FC, CC, and MPS using the Taylor K-2041 kit (R-0867 Deox Reagent) in conjunction with the K-2006. I've noticed that FC stayed pretty constant all week (FC = ~2.4 and CC = .4) when just adding MPS after soaks and starting with chlorine on Sunday and a level of 3.6 ppm Monday morning. We're soaking about 1 1/2 people hours every other day and adding 4 tbsp of MPS (32.2%) each time.

Questions:

• I expected that FC would go down fairly quickly over the week with just using MPS, ozone, and UV (and some sunlight). Any ideas why the FC level stays high? It appears that MPS is registering as FC. Do you agree and is this expected?
• When doing the FC, CC, TO tests, there is a point where the sample water is white - but not the whitest - and it takes an extra drop to get it bright white. I presume I count that last drop. Sometimes, after waiting 15 seconds, the bright white can even revert a bit to not pure white. Do I ignore this or add yet another drop?
• My wife and I noticed a faint "pool smell"and it is objectionable, and we never used chlorine in our previous spa. The only way I was able to get FC down near zero (.2) along with the offending odorous CC (.2), was not adding any MPS for two days. I'm confused how CC dropped only without the addition of MPS (or chlorine).
• MPS level stays between 3 - 5 ppm. Anyone have a target range of what residual we should aim for? This seems high to me and I'm considering cutting it in half. I know and have been using the rule of 7 tsp of 43% MPS per person soaking hour, but perhaps the ozone and UV and doing their job?

Background:

• I'm about 10 days in to using my spa. I started with a few doses of dichlor and switched to MPS after soaks and plan dichlor / bleach once a week to supplement.
• I'm up to a CYA level of 25 according to the formula 10 FC = 9.1 CYA (from Pool Math) and plan on stopping at 30.
• TA = 50, CH = 150, Borates = 50, pH pretty steady at 7.6.
• I had to add ~35 gallons after a week - I presume due to hot (90s) and dry days.

 

[DrewLG]

I've been tracking FC, CC, and MPS using the Taylor K-2041 kit (R-0867 Deox Reagent) in conjunction with the K-2006. I've noticed that FC stayed pretty constant all week (FC = ~2.4 and CC = .4) when just adding MPS after soaks and starting with chlorine on Sunday and a level of 3.6 ppm Monday morning.

I'm not sure I follow. When did you add chlorine? And what days did you measure FC and CC (and KMPS), and what were those measurements?

If you get the PoolMath app for iOS or Android (and sign in to it with your TFP username), you can link your logs of chemical additions and measurements to your TFP profile, which will make it easier for people here to give advice. Click the PoolMath Logs button in my profile to see what I mean.

I expected that FC would go down fairly quickly over the week with just using MPS, ozone, and UV (and some sunlight). Any ideas why the FC level stays high?

The KMPS that you're using is oxidizing organic contamination. Without those contaminants to react with, the free chlorine in the water doesn't turn into combined chlorine. So more free chlorine remains available. And if the hot tub is usually covered during the day, the chlorine isn't burned off by UV.

It appears that MPS is registering as FC. Do you agree and is this expected?

Without the deox reagent, KMPS will register as CC. Are you performing the tests correctly with that reagent? The sequence (using 10ml samples for 0.5ppm resolution) is:

• Setup for FC/CC tests:
  • 10 ml of pool water in a clean vial.
  • Prepare a pipette with 0.5ml of R-0867 Deox reagent.
• Prepare for FC test and kill any KMPS interference:
  • Add one heaping dipper of R-0870 DPD powder to the vial and stir, then immediately add the R-0867 and stir.
• Test for FC:
  • Without delay, begin adding R-0871 at around one drop per second, counting drops, until the solution turns completely colorless (i.e., until you add a drop and get no further color change -- don't count that last drop).
• Prepare for CC test:
  • Immediately add 5 drops R-0003 DPD reagent and stir.
  • Wait one minute. While you're waiting, multiply the number of R-0871 drops by 0.5 to get FC concentration in ppm. Write that down.
• Test for CC:
  • Add R-0871 again, counting drops, until the solution turns completely colorless again. Multiply number of drops by 0.5 to get CC concentration in ppm. Write that down.
• Setup for TO (total oxidizer) test:
  • Rinse the vial and refill with another 10ml of pool water.
• Prepare for TO test:
  • Add one heaping dipper of R-0870 DPD powder to the vial and stir.
  • Add 5 drops R-0003 DPD reagent and stir.
  • Wait one minute.
• Test for TO:
  • Add R-0871 yet again, counting drops, until the solution turns completely colorless. This test should require at least as many drops as the FC and CC tests combined, because TO is the sum of FC, CC, and KMPS.
  • Multiply number of drops by 0.5 to get Total Oxidizer (TO).
• Calculate KMPS:
  • Calculate TO - FC - CC. The result is KMPS concentration in ppm.

When doing the FC, CC, TO tests, there is a point where the sample water is white - but not the whitest - and it takes an extra drop to get it bright white. I presume I count that last drop.

Yes.

Sometimes, after waiting 15 seconds, the bright white can even revert a bit to not pure white. Do I ignore this or add yet another drop?

Ignore. The steps in the FC test need to go quickly -- you'll notice that the Taylor instructions say "IMMEDIATELY" a lot. You're done when the solution FIRST turns completely colorless.

My wife and I noticed a faint "pool smell"and it is objectionable, and we never used chlorine in our previous spa. The only way I was able to get FC down near zero (.2) along with the offending odorous CC (.2), was not adding any MPS for two days. I'm confused how CC dropped only without the addition of MPS (or chlorine).

My experience is with pools, not hot tubs, so the idea of targeting 0.0 FC is foreign to me. If that's really a thing with hot tubs, maybe someone else here can offer knowledgeable advice.

While you wait for that, though, I can make something up:

If the hot tub is outdoors, the offending odors probably blow away within a day of being created. But new CC odors are created whenever FC and organic contaminants get together, and as discussed above, your KMPS dosing was prolonging the life of the FC in your water (and apparently not COMPLETELY eliminating contaminants, so there was still a slow FC --> CC reaction).

When you stopped using KMPS, the remaining FC quickly combined with contaminants to produce CC, and then the CC odors quickly faded.

You could probably also make the CC odors go away by going the other direction and using MORE (or more frequent) KMPS, in order to more completely eliminate the organics so there won't be any available to combine with FC.

• MPS level stays between 3 - 5 ppm. Anyone have a target range of what residual we should aim for? This seems high to me and I'm considering cutting it in half.

KMPS is not a sanitizer and will not kill bacteria or other pathogens; it's simply a fast-acting oxidizer that can eliminate organics so the FC won't have to do that and can instead work to disinfect the water. So when I use KMPS in my pool, I don't aim for ANY residual -- it's just, boom, oxidize whatever bather waste or pollen or whatever is in the pool, make the water sparkly, then go away.

My dosage is one pound for my 8000 gallon pool, broadcast over the entire surface. I typically measure 1ppm KPMS the next day, then 0ppm the day after.

But again, I don't know whether hot tubs do it differently.

I'm up to a CYA level of 25 according to the formula 10 FC = 9.1 CYA (from Pool Math) and plan on stopping at 30.

It would be nice to confirm your calculations by performing the CYA test in your K-2006. Just to be sure.

 

[contentedPilgrim]

I'm not sure I follow. When did you add chlorine? And what days did you measure FC and CC (and KMPS), and what were those measurements?

If you get the PoolMath app for iOS or Android (and sign in to it with your TFP username), you can link your logs of chemical additions and measurements to your TFP profile, which will make it easier for people here to give advice. Click the PoolMath Logs button in my profile to see what I mean.

First off, thanks for your detailed reply. I waited a day to respond to get another day's worth of data points.
The PoolMath app only allows for 3 entries before requiring a paid subscription. The best I can do is my spreadsheet.

The KMPS that you're using is oxidizing organic contamination. Without those contaminants to react with, the free chlorine in the water doesn't turn into combined chlorine. So more free chlorine remains available. And if the hot tub is usually covered during the day, the chlorine isn't burned off by UV.

Makes sense... but the tub also has UV that runs for 8 hours per day. I would expect it to have some impact.

Without the deox reagent, KMPS will register as CC. Are you performing the tests correctly with that reagent? The sequence (using 10ml samples for 0.5ppm resolution) is:

Yes, I have followed instructions - only using the 25 ml sample with 1 drop = 0.2 ppm.

My experience is with pools, not hot tubs, so the idea of targeting 0.0 FC is foreign to me. If that's really a thing with hot tubs, maybe someone else here can offer knowledgeable advice.

My goal is for 0.2 - 0.5 ppm FC. I used a hot tub for 10+ years with no chlorine (except at startup). Reading this site has altered my approach a bit. My new routine is to use chlorine once a week (at 6 ppm) to kill pathogens and then shoot for a residual of 0.5 or less. The Nature2 + MPS (+ UV) + Chlorine bound up with CYA, will handle (for me) everything in between weekly doses of Chlorine. I read about 100 posts on this site and others which proclaim only Chlorine or Bromine are true sanitizers. Based on 10 years of experience with Nature2 + MPS, I feel comfortable deviating from the TFP gospel.

While you wait for that, though, I can make something up:

If the hot tub is outdoors, the offending odors probably blow away within a day of being created. But new CC odors are created whenever FC and organic contaminants get together, and as discussed above, your KMPS dosing was prolonging the life of the FC in your water (and apparently not COMPLETELY eliminating contaminants, so there was still a slow FC --> CC reaction).

When you stopped using KMPS, the remaining FC quickly combined with contaminants to produce CC, and then the CC odors quickly faded.

You could probably also make the CC odors go away by going the other direction and using MORE (or more frequent) KMPS, in order to more completely eliminate the organics so there won't be any available to combine with FC.

Yes, I've contemplated this and it makes sense. I will give it a try.

KMPS is not a sanitizer and will not kill bacteria or other pathogens; it's simply a fast-acting oxidizer that can eliminate organics so the FC won't have to do that and can instead work to disinfect the water. So when I use KMPS in my pool, I don't aim for ANY residual -- it's just, boom, oxidize whatever bather waste or pollen or whatever is in the pool, make the water sparkly, then go away.

My dosage is one pound for my 8000 gallon pool, broadcast over the entire surface. I typically measure 1ppm KPMS the next day, then 0ppm the day after.

But again, I don't know whether hot tubs do it differently.

Thanks for the reference of 1ppm MPS. My line of reasoning is that if I'm above a certain level, I've added enough to handle oxidation of bather waste and to prevent chlorine combining to create CC. Seems like shooting for 2 ppm is reasonable. My last dosing (today) got me there.

It would be nice to confirm your calculations by performing the CYA test in your K-2006. Just to be sure.

The K-2006 only starts reading at 30 ppm. I was waiting until I got close to 30 by the formula before testing. I'm at 24, so that should be next Sunday.