The impact of MPS and CYA on various tests?

[AlwaysConfused]

Hi.

I apologize, I have tried searching past forums because it seems this *must* have been answered before.

Background: New owner, 350g. I use MPS and dichlor. Water smells clean (i.e., like water, hint of Cl smell). Water is clear.

Aquachek Pro Strips read ~7ppm TC, ~2ppm FC (yeah, I know -- strips)
OTO reads ~2 ppm Cl (read at ~20 s after reagent addition)

I am not sure of my CYA levels, I am guessing ~30-50, but, I was using dichlor per vender instructions before I knew to track total dichlor addition.
My thought was to use dichlor/bleach(after appropriate cya levels reached) to maintain FC and to use MPS after bathers and as a weekly shock.
Instructions from bottle and vendor suggest 1.5oz per application of MPS, but, I am thinking that is quite high now...

I think I currently have a problem figuring out my Cl levels....

** My fear is that I currently have no Cl and I am reading MPS as a false positive on both tests
** OR that I have high CYA that is sequestering the Cl and it is reading at TC (or slow color development on OTO)

QUESTIONS (please):
Will MPS still affect Cl readings 12 hrs after addition?
How does MPS read on OTO vs FAS-DPD?
How long will MPS remain affecting tests?

I know CYA attenuates Cl
How does CYA affect the OTO/FAS-DPD tests?
-If I add bleach, will it combine with CYA and read as TC vs FC?
-What will the impact be on OTO and/or the test strip reads?


I guess a summary question is:
I have strips that read TC/FC. I have OTO. I have a K2006 kit on order
In each of the measurements, when it says it is measuring "FC" or "TC" or "CYA" etc
How much is it really measuring MPS/FC/CC/CYA??

Thanks! :blah:

 

[RobbieH]

CYA does not affect your FC (CL) tests.

TC = FC+CC. So don't confuse TC and FC, the are not the same unless CCs are 0. It's important to know all three unless you are absolutely sure you don't have issues, then you can just concentrate on FC.

If your strips are correct (unlikely) your CC is 4, which indicates a problem.

 

[Isaac-1]

MPS reads as CC on Chlorine tests, and there is a special Taylor test available to correct for it when using the K-2006, I have it, but rarely use it as I have an indoor pool and sometimes use MPS for supplemental oxidation after large groups of swimmers. In my case it can take 2 or 3 days for the MPS to stop effecting the chlorine readings, I am not sure if this would be different with outdoor pools. As to the CYA it should have no effect on your chlorine test readings, even though it does act as a chlorine buffer. Now a question for you, Why would you want to do this instead of following the TFPC suggested pool care system, do you have some special need for supplemental oxidation, very high bather loads, etc? If not there is likely no need to use MPS in a typical residential pool, and it is just wasting money.

Ike

 

[chem geek]

It sounds like this is a 350 gallon spa, not a pool. Nevertheless, it would make more sense to use the Dichlor-then-bleach method instead of MPS unless one has the Nature² system providing silver ions in which case MPS would work as a disinfectant with the silver ions. Which way go to depends on frequency of spa usage, whether there is an ozonator, and preference for chlorine or non-halogen. Bromine is another option.

 

[AlwaysConfused]

Thank you all for the replys!
To make sure I understand..
RobbieH: CYA will NOT make FC read like CC or vice versa in either strips or OTO or FAS DPD tests
Issac-1: As I understood, MPS was "gone" in like 30 min as far as bathers were concerned, but, will affect tests up to 2-3 days.
MPS reads as CC... does that mean in an OTO test it slowly develops color? Would it have affected my strip reading of FC?

Chem Geek: I do have the nature2 system. I was NOT aware that nature2 + MPS worked as a disinfectant! No ozonator. I do have a UV bulb (clearwave?)

My thought of:
using dichlor as needed to keep FC in the 3ppm range
MPS after bathers
Was based on the idea that MPS was a good oxidant for bather waste, would mean that CYA always was added with Cl. I would not have to weekly shock with Cl since MPS would deal with the CC and bather waste.

Spa usage is 3-4 times a week, 1-3 users, ~1hr

 

[chem geek]

With your fairly frequent spa usage and no ozonator, the Dichlor-then-bleach method would work for you in which case the Nature² is superfluous. MPS does not do any better job at oxidizing bather waste than chlorine and in fact the opposite is true in that Nature² + MPS spa users usually have to add chlorine once a week or so to keep the water clear.

You are correct that CYA doesn't affect the chlorine tests. Basically, the chlorine gets released from CYA in the time of the test to show up as FC. If MPS gets used up oxidizing bather waste, then it will not show up in test strips. If you see MPS in test strips or as CC, it is really there, perhaps because not all of it got used up oxidizing bather waste. MPS will show up in the OTO test since that tends to show up most oxidizers and it may not take long to show up.

 

[AlwaysConfused]

Thank you again... ok, I have 2 days of no use and no adding MPS.. The strips showed ~0.5ppm TC and 0.5ppm FC -- So, I am guessing that I was reading MPS as was suggested. (I am waiting on my taylor kit to arrive)

I added 8.5% bleach to 3ppm and will read again tonight or tomorrow.

Two more questions, please

It seems that residual MPS lasted longer than added Cl seems to last. Would it make sense to use MPS/Nature2 as the primary disinfectant if my bather load is reduced (say 2-3x/wk 1 user)... As high usage it seems that bleach is cheaper/faster. At low usage it seems MPS is easier maintenance.

2nd question.. Im trying to remember, I think I saw a point that in using Cl one should add ~7.5ppm Cl/batherhour after soaks. Is that correct? and if one does that, does one not need to do weekly shocks?

Thank you again. Your clarifications on the effects of CYA/MPS on tests explain a great deal.

I am also adding this link which talks about MPS+silver http://www.poolspaforum.com/forum/?showtopic=11366
since your post is the first I learned about it, I never thought to google that before..

 

[chem geek]

It seems that residual MPS lasted longer than added Cl seems to last. Would it make sense to use MPS/Nature2 as the primary disinfectant if my bather load is reduced (say 2-3x/wk 1 user)... As high usage it seems that bleach is cheaper/faster. At low usage it seems MPS is easier maintenance.

You understand this perfectly. You still might be able to use chlorine with somewhat higher dosing after each soak even with 2-3x/week usage since you don't have an ozonator. If your daily chlorine loss rate at hot spa temperatures were 25% per day, then 4 ppm FC would go to 3 ppm FC to 2.25 ppm FC and then to 1.7 ppm FC after 3 days (to 1.3 ppm FC after 4 days) for the start of your next soak and that would be OK. It's if you tried to go an entire week where it would be difficult with chlorine unless you raised it significantly (say, to 10 ppm FC which would be 1.3 ppm FC after 7 days).

It's up to you since you can certainly use the MPS (with silver ions from Nature²) which lasts longer (though costs more) whenever you think there will be too much time in between soaks for the chlorine to last.

2nd question.. Im trying to remember, I think I saw a point that in using Cl one should add ~7.5ppm Cl/batherhour after soaks. Is that correct? and if one does that, does one not need to do weekly shocks?

The ppm chlorine for bather load is a function of spa size. It's roughly 7 ppm FC per person-hour only in a 350 gallon spa, which happens to be the size of your spa. The rough rule-of-thumb that is independent of spa size is that every person-hour takes 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach (3-1/2 fluid ounces of 8.25% bleach) or 7 teaspoons of non-chlorine shock (43% MPS).

If you properly dose with chlorine after a soak to handle the bather load and you properly dose with chlorine in between soaks to maintain a background level of chlorine (if the time between soaks is long enough to require that), then there is no need to shock the spa on a regular basis. It's the same principle as in maintaining a pool. If the chlorine level is properly maintained relative to the CYA level, there is no need for any regular shocking.

 

[AlwaysConfused]

Your rule of thumb for dosing is now in my notebook, thank you!

With regards to the testing -- If I use MPS at times and Cl (bleach) at others and MPS cross reacts with the Cl test, is the level of sanitizing about the same for the same color shift in the test?

For example, if I want a target of 3ppm FC and I get the same color reading for some concentration of MPS, am I ok? i.e., for the same color read from some level of MPS, is that the same sanatizing efficacy as that color when it is truly from FC?


(I ask because, for my roommate, it is easier for her to deal with the MPS powder than to pour out the appropriate amount of bleach, but, I will still want to monitor the level of residual sanitizer)

 

[chem geek]

MPS by itself does not disinfect (at least not nearly as quickly as chlorine). It is MPS in conjunction with silver ions as with the Nature² system that is an EPA-approved disinfectant. MPS alone is not.

If your roommate does not want to deal with bleach, she could dose with Dichlor, but just be aware that this will build up the CYA level so will require a water change sooner than if you used mostly bleach. For every 10 ppm FC added by Dichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.

 

[AlwaysConfused]

With the roommate MPS method, I was planning on keeping the extra (minimal) expense of the Nature2 system so that the MPS would be effective.

In that light, do you think the measured MPS as it cross reacts in a Cl test will be a good way to measure if I have enough MPS?

e.g., if I am targeting 3ppm Cl and read 3ppm from MPS, is that sufficient (assuming the silver ions are present)

Yes, I was afraid to just let them do the dichlor for the CYA buildup.

Thank you again and Happy Thanksgiving!

 

[chem geek]

OK, then that's fine. Yes, you can use the FC+CC reading in the FAS-DPD chlorine test to figure how much total chlorine and MPS you have and that's a reasonable measure. You normally don't have CC except after a soak so if you measure before a soak or sufficiently long (> 8 hours) after a soak then that should work.

I'm not as confident in terms of using the OTO test for measuring both. You might do a test comparing your FAS-DPD readings against the OTO test when using MPS to be sure.