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Thread: Almost time to switch from MPS/Dichlor to Bleach

  1. Back To Top    #1

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    Almost time to switch from MPS/Dichlor to Bleach

    Hi all,

    Our CYA level has built up to about 30 (31.5 by calculation) using Replenish (which is MPS and Dichlor) and a Nature 2 stick. I have some questions before we switch:

    1.) Can we yank the Nature 2 stick, throw it in a ziploc and use it at the start of our next fill? We still have Replenish so on our next fill I'd go back to using it to build up the CYA level. The stick only has 1.5 months on it so it seems bad to waste it.
    2.) Today's testing gave us the following levels:
    FC: 2.4
    CC: 0.0
    pH: 7.0 (but after aerating for 20 minutes it came up to 7.6)
    TA: 60
    CH: 80

    Before we add the borates (29oz Borax and 14oz of 31.45% Muriatic Acid) are our other numbers ok to start? I'm assuming you add the borates and then let that circulate and adjust TA and pH as needed?

    Once that's all set, I guess we just keep the FC in the 2-4 range (12ppm for shock level) per the chart and then use Dichlor (we have Spa 56 available) once a month to account for CYA loss.

    I'll have to figure out what we do if we're going to be away for more than 2 or 3 days since we don't have anyone nearby to add bleach but I'll cross that bridge if it ever happens once I know a 24 hour loss rate.

    thanks in advance!
    -------------------------
    Jacuzzi J-385. New December 2014. 500 gallons, no ozonator. Has ClearRay system (if that matters).

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    Re: Almost time to switch from MPS/Dichlor to Bleach

    I don't know if a Nature2 cartridge can be removed and then replaced later.

    It sounds like you have Borax and acid. In the future, it's usually easier to use boric acid which is only a little acidic. When you add the Borax and acid, split the dosing into at least 3 if not 4 parts so your pH does not swing too much. I'd start with the acid, then Borax, back and forth to avoid the risk of scaling though most important is to split up alternating dosing. And yes, you adjust the pH and TA at the end, though if you wanted your TA down to 50 ppm you should do that now before adding the borates since it's easier to do now.

    As for the FC, many people prefer to start their soak with 1-2 ppm FC so you can time things to maintain more in between soaks and then let it drop a little before your soak. Up to you. The key is to not have zero chlorine at all in between soaks and to add whatever is needed to oxidize bather waste after each soak. And yes, use Dichlor for a day or so once a month to add around 5 ppm CYA.

    Once you figure out your 24 hour loss rate, which without an ozonator should be less than 25% per day, you should be able to just turn down your water temperature, elevate the chlorine level, cover the spa, and be good for several days with no problem, even one week if you elevate enough. 10 ppm FC after 7 days with 15% daily chlorine demand would result in 10*(1-.15)7 = 3.2 ppm FC; with 20% daily chlorine demand it would result in 2.1 ppm FC; with 25% daily chlorine demand it would result in 1.3 ppm FC. So you can usually go one week by just elevating the chlorine level. It's those who have ozonators with 50% or more daily chlorine demand that have trouble since it goes from 10 to 5 to 2.5 to 1.3 to 0.6 to 0.3 to 0.2 to 0.1 after one week.
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  3. Back To Top    #3

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    Re: Almost time to switch from MPS/Dichlor to Bleach

    I don't have the Borax part of it yet, just the MA. Can that be used for other things? If so, I'm fine just keeping that and getting Boric Acid somewhere if it makes the process easier. Isn't Boric Acid an ant powder sold at say Wally World? Or is it not the same thing?

    Interesting that to get the TA from 60 to 50, pool math just says lower the pH to 7.0 - 7.2 with acid, then aerate to bring the pH back up. So the original pH was 7.0 this afternoon when we tested and got the TA of 60 (which is lower than what it had been, prior weeks were 80) and then when I hit the jets and air for 20 minutes, it went up to 7.6 so I'm wondering if I really need to mess with the TA at all. Or if I should just put a bit of acid in it, 1.2oz MA (hey, a use for it!) is what pool math calls for to go from 7.6 to 7.0 on 500 gallons with no borates yet in the water and then aerate.

    Great to know on the FC after 7 days would still be ok! And thanks for that formula. I'll keep it handy for when I figure out the 24 hour loss.
    -------------------------
    Jacuzzi J-385. New December 2014. 500 gallons, no ozonator. Has ClearRay system (if that matters).

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    Re: Almost time to switch from MPS/Dichlor to Bleach

    The MA can be used to lower the pH and TA. The MA won't go bad. And yes, boric acid is found in insect powder, but you can buy it in bulk at relatively low cost from Duda Diesel or The Chemistry Store.

    Yes, the process to lower the TA is to add acid at low pH with aeration. The full procedure is described in the Pool School article on how to Lower Total Alkalinity. It works because acid lowers both pH and TA while the outgassing of carbon dioxide from the water raises the pH with no change in TA. The combination therefore lowers the TA. The outgassing is faster with more aeration and at lower pH.

    If you do not have the TA lower, then the pH will rise more quickly and you will use more acid over time. Having a lower TA lowers the amount of carbon dioxide outgassing. TA is mostly a measure of bicarbonate in the water and bicarbonate is in equilibrium with carbon dioxide in the water. The water is over-carbonated. I'd add the acid, aerate, and keep at it until the TA is lower at 50 ppm. You can see how much total acid that will take by looking at the "Effects of adding chemicals" section in PoolMath. The relationship of how much TA drops for a given amount of acid in a fixed volume is a constant and is independent of the pH and TA level.
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    Re: Almost time to switch from MPS/Dichlor to Bleach

    Just ordered 5lbs of Boric Acid from Duda so I'll get going on this once that's arrives.

    Looks like 1.2 - 1.3oz will get the TA Down by 10 and the pH down by 6.2 tho I might do the acid demand test from my kit to check that (and it's finally a use for that test). But then I'll aerate and get it up the 7.6'ish again on the pH and then TA should be 50. What happens over time tho? I guess this part is confusing me where you said:

    "It works because acid lowers both pH and TA while the outgassing of carbon dioxide from the water raises the pH with no change in TA. The combination therefore lowers the TA. The outgassing is faster with more aeration and at lower pH."

    With use tho and the outgassing, won't pH just keep creeping up as we use it? We don't deal with sliding pH now with the Replenish.
    -------------------------
    Jacuzzi J-385. New December 2014. 500 gallons, no ozonator. Has ClearRay system (if that matters).

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    Re: Almost time to switch from MPS/Dichlor to Bleach

    .................. pH . TA
    Add Acid ...... - ... -
    Aerate ........ + ... 0
    -----------------------
    NET RESULT . 0 ... -

    The pH does not keep going up because your acid additions lower it. You don't just add acid once. You keep adding acid to have the pH be low and you aerate, so the combination of the two just has the TA drop.

    As for use and outgassing, yes the pH would climb, BUT outgassing is much slower when the TA is lower and the pH higher (see this chart that shows the degree of over-carbonation of water at various TA and pH levels). So the bottom line is that the pH rise and especially the amount of acid you need to add is less. The thing to keep in mind is that TA is BOTH a pH buffer that resists changes in pH AND it is a SOURCE of rising pH due to carbon dioxide outgassing (TA is a mostly a measure of bicarbonate in the water and bicarbonate is in equilibrium with carbon dioxide in the water and that can outgas).

    For additional pH buffering that does not contribute to pH rise, you use 50 ppm Borates. This buffers the pH even more strongly as the pH gets higher so is an ideal complement to the carbonate pH buffer system, but has the significant advantage that it does not outgas carbon dioxide so does not contribute to rising pH.
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    Re: Almost time to switch from MPS/Dichlor to Bleach

    Ah ok, I think I missed the part where I'd have to periodically add acid to keep the pH low since I don't have to do anything like that now with the Replenish.

    So when's the best time to test the pH? We generally do testing on Sundays. So if we're in Saturday nite, it's aerating.... will it have enough non-aerated time by say mid morning Sunday to get a true read? Or would pH remain in the aerated/higher range (i.e. 7.6) longer than that and if we added acid, we could add too much thinking we need to get it down a bunch?
    -------------------------
    Jacuzzi J-385. New December 2014. 500 gallons, no ozonator. Has ClearRay system (if that matters).

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    Re: Almost time to switch from MPS/Dichlor to Bleach

    Adding acid to keep the pH low is ONLY during the short-term process of lowering the TA. After that hopefully you don't need to add very much acid.

    Leisure Time Replenish is MPS which is acidic and is why you didn't need to separately add any acid. So yes, when using bleach you may need to use some acid on occasion to keep the pH reasonable, but if you lower the TA level to around 50 ppm and you use 50 ppm Borates you may find your pH remains reasonably stable perhaps at 7.7 or 7.8, but it will depend on the amount of aeration in your spa.
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    Re: Almost time to switch from MPS/Dichlor to Bleach

    oh oh oh!! ok now I get it! Thanks for clearing that up for me. The Boric Acid should be here by Thursday so I can sort things out then. Might start lowering the pH on Wednesday so I'm reading to go when the Boric Acid arrives.
    -------------------------
    Jacuzzi J-385. New December 2014. 500 gallons, no ozonator. Has ClearRay system (if that matters).

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    Re: Almost time to switch from MPS/Dichlor to Bleach

    One other quick question. Lets say the aeration is keeping it in the 7.7 - 7.8 range. What happens when we aren't in it for several days
    (no aeration). Is there risk that the pH drops too much and becomes too acidic and damages the plumbing and whatnot? I think the spa does do a daily check cycle where the jets are running, tho the air part isn't unless we leave them on, so maybe that compensates enough.
    -------------------------
    Jacuzzi J-385. New December 2014. 500 gallons, no ozonator. Has ClearRay system (if that matters).

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    Re: Almost time to switch from MPS/Dichlor to Bleach

    Yes, the pump does run from time to time, but the air shouldn't be. It is unlikely that PH would drop below 7 in a few days and if it did it wouldn't damage anything.
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    Re: Almost time to switch from MPS/Dichlor to Bleach

    Ok thanks for that info. I'm thinking if we're on vacation or something.
    -------------------------
    Jacuzzi J-385. New December 2014. 500 gallons, no ozonator. Has ClearRay system (if that matters).

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    Re: Almost time to switch from MPS/Dichlor to Bleach

    Unless acidic sources of chemicals are added, the pH should not drop. If there is no aeration, the pH should be stable. Chlorine usage/consumption is acidic but adding chlorine bleach has the pH rise so it just ends up back where it started. So going on vacation for a week should be fine (with no ozonator). You'd lower the water temperature which would lower the daily chlorine loss rate. You can't go much more than one week like this, however. For anything longer, you'd dump the spa (i.e. do a water change so refill when you got back home, using Ahh-Some to get rid of biofilms).

    I forgot to mention that you should get Ahh-Some that you should use just before changing the water and also for a new or used spa before using it for the first time.
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