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Thread: Chlorine and MPS in my spa?

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    Chlorine and MPS in my spa?

    Ok, so I'm not a complete noob, but I do have a question about MPS.

    I have a fresh fill in my 400 gallon spa. I added 80ppm CYA and have been using bleach to sanitize.

    Is there a reason to add MPS? And if so, when do I do it? It says it's a non-chlorine oxidizer, but isn't chlorine an oxidizer too? So why add MPS?

    Does MPS go away after a day or two like chlorine bleach does? Or does it stay like CYA?

    Last, I used borax in my water before the refill and I noticed that the water was prone to get sudsy. I feel this is more from the spa additives rather than bather waste. We haven't had lots of sunscreen on and really the bather load is light. I'm cautious about re-adding any borax into the water. But I think I need to to help the chlorine stay in the hot water longer, or to be more effective at lower concentrations.

    Thanks for any help.

    -steve
    20,000 Gallon, Vinyl Liner
    Hayward Sand Filter
    South Mississippi

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    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
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    12,082

    Re: Chlorine and MPS in my spa?

    For a spa, I'd target 30 ppm CYA since you want a higher active chlorine level though you can do that on your next water change -- the CYA level will drop slowly around 5 ppm per month (maybe faster at your higher CYA level). There isn't any reason to add MPS if you are using chlorine since chlorine is generally a better oxidizer for most bather waste. If you do use MPS, it gets used up as chlorine does oxidizing bather waste.

    If you are experiencing foaming, raise your CH level to 120-150 ppm and try to get people to rinse off so they don't introduce soaps or lotions into the water. As for the borates, they help to buffer the pH, but don't do anything to keep chlorine in the water longer or to be more effective. You may be thinking about borates for pools where they are a mild algaecide so can act as insurance in case the chlorine level gets too low, but for spas algae is rarely an issue so the borates are really there for helping to prevent the pH from rising as quickly.

    You can read more in Using Chlorine in a Spa though I would get your TA closer to 50 ppm rather than 80 ppm to help keep the pH from rising.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  3. Back To Top    #3

    Re: Chlorine and MPS in my spa?

    Great, thanks for the information.

    Knowing what I've learned from TFP, let me ask another question. Say chlorine is used attacking bacteria or other nefarious stuff in the water. This takes FC and ultimately ends up as CC, correct? This CC doesn't just go away, right? Isn't that the reason most people shock, to get rid of the CC?

    Does adding MPS once a week lower the CC as well? I have an ozonator, but I'm sure it's not sufficient enough to really be relied upon to do any duty exclusively.

    Thanks.
    20,000 Gallon, Vinyl Liner
    Hayward Sand Filter
    South Mississippi

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    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: Chlorine and MPS in my spa?

    The amount of bacteria shed from fecal matter and skin is way too small to be detected as any sort of CC. The CC you might measure would be from the ammonia in your sweat and urine which would quickly react with chlorine to form monochloramine or it could be from the urea in your sweat and urine which more slowly reacts with chlorine to form monochlorourea. Just having chlorine present will continue to oxidize these chemicals getting rid of the CC. This process is accelerated in an outdoor pool exposed to sunlight since the UV in sunlight breaks down chlorine initially into hydroxyl free radicals that are very reactive and probably help control urea concentration. For a spa, all chemical reactions are sped up by the higher temperatures and it seems that the oxidation of urea occurs much more quickly than seen in room temperature experiments.

    The other source of measurable CC would be algae growth if you don't have a high enough FC/CYA ratio, though that is not normally seen in spas. As for bacteria, it takes so little chlorine to kill most bacteria that you would have to have a near-zero chlorine level to have such bacteria grow, though once it starts it can form biofilms that are then more resistant to getting killed by chlorine. So if a pool or spa is improperly managed and the chlorine gets to zero for too long, then one can get enough bacterial growth to also show up as CC or show up as higher-than-normal chlorine demand.

    A properly managed outdoor residential chlorine pool does not normally need to be shocked. The constant maintenance of a proper chlorine level continuously oxidizes bather waste preventing CC from building up. In some sense, it is being continuously shocked if by "shocked" one means oxidizing bather waste and killing algae and bacteria. As for a spa, it too does not normally need to be shocked but heavier bather loads especially if one is not clean may require shocking as needed.

    MPS can oxidize some chemicals, but doesn't oxidize everything that chlorine does (and vice versa). It can help prevent CC formation for some chemicals (such as creatinine and some amino acids), but is not normally necessary. In a spa using chlorine, it is not normally needed.

    As for an ozonator, it is helpful in a spa that is used every day or two since ozone can oxidize some bather waste, but in a spa used only once a week or so, ozone ends up using more chlorine since ozone reacts with chlorine.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Chlorine and MPS in my spa?

    Awesome. Thanks so much.
    20,000 Gallon, Vinyl Liner
    Hayward Sand Filter
    South Mississippi

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