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chem geek

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  1. While a saltwater chlorine generator will regenerate chlorine (hypochlorous acid) from salt (chloride ions), it should not regenerate significant amounts of MPS (monopersulfate) from sulfate ions, mostly because the level of sulfate is so low so the primary reactions are generation of chlorine and of some oxygen gas.

    The monopersulfate should slowly go away when it oxidizes chemicals in the water, but if you want to have it go away faster than an easy way to do that is to dechlorinate the water since that will get rid of the monopersulfate as well.  You can dechlorinate with standard sodium thiosulfate from a pool store or you can use hydrogen peroxide (such as in Baquacil Oxidizer -- careful: NOT CDX or Sanitizer).  You don't need to dechlorinate for very long -- with good circulation an hour should be sufficient -- and then you add chlorine back to prevent bacteria and algae growth.  Don't use the pool when there is no chlorine in it.

    You might have monopersulfate at low or zero levels already.  The way to test for it is to use a Taylor FAS-DPD chlorine test, such as in the K-2006 or K-1515 and then get the K-2042, OR you can just get the K-8031 if you are only interested in monopersulfate and don't want an accurate chlorine test.

  2. How often to clean a filter depends a lot on how much you use the spa and your cleanliness when using the spa.  If you don't use it often or rinse off skin oils and don't use lotions then there won't be a lot getting caught in the filter.  You'll still have your sloughed off dead skin cells.  So this is something you need to judge by seeing how dirty the filter is when you clean it at a certain frequency and also how your water looks since the purpose of filtration is to keep the water clear.

    As for a water change, here again it's mostly about water clarity from a buildup of unoxidized organics including those small enough to not coagulate or adhere to the filter.  The other effect of going longer is that there is a salt buildup over time.  Higher salt levels can be more corrosive.  For every 10 ppm FC added by bleach, it also increases sodium chloride salt by about 17 ppm so you can calculate roughly how much you've built up over time.  As for when to change due to salt, you can go to 1000 or 1500 ppm and be fine.  Much more than that increases your corrosion risk though saltwater chlorine generator pools have around 3000 ppm.  The corrosion risk is greater if your spa heater has a copper heat exchanger instead of a more corrosion-resistant cupro-nickel or titanium heat exchanger.  The hotter temperates accelerate corrosion rates and chemical reaction rates in general.

    As a rough rule-of-thumb, most Dichlor-then-bleach users are able to go about twice as long as Dichlor-only users and when they do change the water it's not as dull since the change is not as noticeable.  The standard industry Water Replacement Interval (WRI) in days is (1/3) x (Spa Size in Gallons) / (# of bathers per day) though this is probably assuming a roughly 20 minute soak time so the formula is really (1/9) x (Spa Size in Gallons) / (# of person-hours per day).  Doubling that for Dichlor-then-bleach would be (2/9) x (Spa Size in Gallons) / (# of person-hours per day) as a rough rule-of-thumb, but if you are happy with your water and want to go longer and the salt hasn't built up too high, then that's fine.

    If you were soaking every day and most of your chlorine usage was from soaking, then if I assume a 350 gallon spa and roughly 7 ppm FC per person-hour in that volume then we have (2/9) x (350) / (1) = 78 days so the salt buildup would be 78*7*17/10 = 928 ppm.  If instead you use the spa only on weekends, then you'd go a lot longer but there would be additional salt built up in between soaks.  Let's say it's 2 person-hours per week, then that's (2/9) x (350) / (2/7) = 272 days.  272*7*(2/7)*17/10 = 925 ppm which (with rounding errors) is the same as before because of the way things cancel out, but we need to add in the salt in between soaks so let's assume 1 ppm FC per day for the 5 days per week so that's an additional 272*1*(5/7)*17/10 = 330 ppm for a total of 1255 ppm.  So still less than 1500 ppm.  This shows that the rough rule-of-thumb of double the standard industry WRI is reasonable, though again you could go longer if you like.

  3. Yes, the CYA level of roughly 30-40 ppm (50 ppm is OK but I wouldn't go higher than that) is needed to moderate chlorine's strength.  The active chlorine level is proportional to the FC/CYA ratio though in hot water spas the absolute level is higher than in cooler water.  The reason people say that bleach would be damaging to spas is that if you were to use ONLY bleach with no CYA in the water at all, then the active chlorine (hypochlorous acid) level would be too high and would oxidize equipment more readily.  It would also outgas faster and oxidize the spa cover faster.

    At a pH of 7.5, the hypochlorous acid level with 5 ppm FC and 30 ppm CYA at 104ºF (40ºC) is 0.34 ppm.  With 50 ppm CYA it would be 0.22 ppm.  With 30 ppm CYA but at a lower 86ºF (30ºC) it would be 0.14 ppm.  If you had no CYA in the water at all, then it would be 2.2 to 2.4 ppm depending on temperature so over 6 times stronger so would degrade equipment and spa covers 6 times faster.

    Don't forget that chlorine slowly oxidizes CYA where in spas it's typically at a rate of around 5 ppm CYA per month so use Dichlor for one day (or so) per month to keep the CYA level up.

  4. Every person-hour of soaking in a hot (104ºF) tub requires roughly 3-1/2 ounces of Dichlor or 3-1/2 fluid ounces of 8.25% bleach or 7 ounces of non-chlorine shock (43% MPS).  4 people for 1 hour would be 14 fluid ounces or nearly 2 cups BUT you can't soak in 104ºF for an hour so your water temp is likely cooler which means you're not sweating as much so would use less chlorine.  Just experiment since the real rule is to add whatever is necessary such that you still have a small residual of chlorine 24 hours later.

    You are correct on the boric acid calculation.

    I'd say 30-40 ppm CYA is reasonable.  I was being overly conservative with all the hot tub rash/itch/lung reports from Dichlor-only (and other) users, but the CYA has to get pretty high (100+ and especially 200+) before those reports were more likely to be seen.  That assumes keeping FC in the 1-4 range since one can technically just raise the FC target as the CYA level climbs but most people don't do that.  Also, with higher CYA comes higher FC demand from oxidizing the CYA itself.  So it's best to just manage the CYA level and I think 30-40 ppm is reasonable and 50 ppm is not going to be a problem.

    FC by itself is not relevant except from a reserve capacity point of view -- that is, in terms of having enough chlorine to not run out.  In terms of effects on equipment, on skin and hair, on rate of disinfection, etc. it's the active chlorine that matters, mainly hypochlorous acid, and that is proportional to the FC/CYA ratio.  You shouldn't need to "shock" or raise the FC high normally, but as you point out for going away you would.  As for your normal 40% chlorine demand, that won't have chlorine last high enough for a week so you need to turn down your spa's water temperature for when you leave as that will significantly lower the chlorine demand.  The following shows the difference starting at 10 ppm FC and having 40% daily chlorine demand vs. 20% chlorine demand.

    Day ....... 40% ...... 20%

    .. 0 ......... 10 ......... 10

    .. 1 ........... 6 .......... 8

    .. 2 ......... 3.6 ........ 6.4

    .. 3 ......... 2.2 ........ 5.1 ..... Limit of being OK for 40% demand (if one wants 2+ ppm FC at all times)

    .. 4 ......... 1.3 ........ 4.1

    .. 5 ......... 0.8 ........ 3.3

    .. 6 ......... 0.5 ........ 2.6

    .. 7 ......... 0.3 ........ 2.1 ..... Limit of being OK for 20% demand (if one wants 2+ ppm FC at all times)

    As for cleaning spa surfaces, other than wiping the main maintenance would be to use Ahh-Some just before you change the water.  If you maintain the spa well you may not need to use it every time but it won't hurt.

  5. Your CYA level is fine to start by just using bleach.  And yes, if your bleach is weaker you just use more.  However, your bleach may have more lye in it proportionately so may mean you'll need to add more acid to keep the pH in check.

    The hardest thing for you will be keeping your pH in check since getting boric acid in Europe is difficult.  If you keep your Total Alkalinity (TA) lower at around 50 ppm then you'll need supplemental pH buffering which is what the boric acid does.  While phosphate buffers are an alternative, if your water is higher in calcium they can precipitate calcium phosphate.

  6. Bleach should not cause foaming so you are probably using "outdoor" or "splashless" or "HE" bleach that have thickeners in it that can cause foaming.  If you us bleach, it should be regular unscented bleach.  Note that you should not use bleach alone and must have some cyanuric acid (aka stabilizer or conditioner) in the water or else the active chlorine level will be too high.  You can use Dichlor initially to build up CYA, say for a week, and then switch to using bleach and only use Dichlor once a month to bring the CYA back up (it slowly gets oxidized by chlorine over time).  See the stickies about this at the top of this forum.

  7. While the original thread is old, the most recent post has prompted me to clarify something about the video that was posted.

    The copper and silver nitrate redox reaction is with SOLID copper mixed with silver nitrate in solution forming copper nitrate in solution and forming solid silver.

    Cu(s) + 2Ag(NO3) ---> Cu(NO3)2 + 2Ag(s)

    Copper Solid + Silver Nitrate ---> Copper Nitrate + Silver Solid

    As shown in the Ingredients list here:
    https://www.walmart.com/ip/Clorox-Pool-and-Spa-Shock-Xtra-Blue-1-lb/41466056#about-item

    the product has 0.26% metallic copper equivalent but as COPPER CITRATE so it's copper ions, NOT solid.  So the reaction you described does not occur.  Furthermore, there is very little copper and silver in the water so not enough to form needles as shown in that video.

    Nature2 for Spas does not have copper in it (Nature2 for pools does).  For spas it has silver and zinc.

  8. No, the 1:1 is for 3% hydrogen peroxide neutralizing the same volume of 6% bleach.  1 fluid ounce of 6% bleach in 350 gallons is 1.4 ppm FC and would take 0.12 ounces weight (about 3/4ths of a teaspoon) to produce that amount of chlorine.  Normally you don't care about the Dichlor weight.  You instead measure your FC, then use a tool like PoolMath to calculate how much 6% bleach is needed for that FC in that volume and then use that amount of 3% hydrogen peroxide (using a somewhat lower amount if you don't want to overdose).

    If one does overdose with hydrogen peroxide it's not a big deal.  Just use additional chlorine to get rid of it.  Even for needing to activate bromide to bromine it just means adding more chlorine until that starts to happen and you start measuring chlorine/bromine.

  9. If you don't measure a disinfectant level then the tub is not being properly disinfected.  What the dealer is hoping is that the ozonator is keeping the water safe and while any water flowing through the ozone system will get disinfected, the ozone does nothing to pathogens not circulating including those growing on surfaces.  If there is sufficient residual ozone making its way into the main tub water, then that would kill pathogens on surfaces but it could also outgas and be a health hazard (ozone is an air pollutant you don't want to breathe).  Most likely, the risk is lower with ozone, but it's safer to always measure a residual of disinfectant.

     

    Normally an ozonator will produce higher bromine readings since it makes bromine from bromide (spent bromine).  Did you start off adding sodium bromide initially?  I'd think you'd have built up enough bromide from the bromine cartridge, but you can always add some Broma-Start or equivalent sodium bromide product and the ozone should then make bromine from it.

     

  10. You can dechlorinate using hydrogen peroxide.  It takes roughly the same volume of 3% hydrogen peroxide to dechlorinate the same volume of 6% bleach so figure roughly how much 6% bleach it would take to get to 50 ppm in your spa and then use that amount of 3% hydrogen peroxide to neutralize it.

     

    I don't know why anyone says not to use hydrogen peroxide to neutralize the chlorine.  The combination reaction results in sodium chloride salt and oxygen gas.  If you overdose the hydrogen peroxide then some chlorine that is added will be neutralized, but if you dump and refill that shouldn't matter since you'll be dumping the hydrogen peroxide.

  11. If the heater is 316 or 316L stainless steel (not 304 stainless steel) then normal chlorine levels should not corrode the heater, especially if you use some cyanuric acid (aka stabilizer or conditioner) in the water with the chlorine.  For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm.

    If you must go with non-chlorine, your options are limited to only two EPA-approved non-halogen options: Baquacil/biguanide/PHMB or Nature2 with MPS (non-chlorine shock).

  12. Non-chlorine shock is more effective at reacting with bather waste before chlorine does.  Using it after doesn't work as well.  However, with the Dichlor-then-bleach method (see sticky threads at the top of this forum) you should be able to use chlorine alone to maintain the water and would add chlorine after your soak in sufficient quantity to oxidize the bather waste and still have a small residual of chlorine for your next soak, if it's the next day.

  13. If the chlorine (or bromine) level is high, then instead of going from green to red, the TA test will go from blue to yellow.  You can either wait for your disinfectant level to get lower or you can use more "A" drops which are probably sodium thiosulfate used to de-chlorinate the sample.

    Even so, taking 30 drops to turn yellow would be a 300 ppm TA which sounds high.  Try again when the disinfectant level is lower (< 10 ppm FC).

  14. That is not true.  What happens is that higher phosphate and nitrate levels provide more food for algae so they can grow faster IF there is insufficient active chlorine to kill it.  You need a Free Chlorine (FC) to Cyanuric Acid (CYA) ratio of at least 5% to be able to kill algae faster than it can grow regardless of algae nutrient levels.

    If you want to maintain a lower than 5% FC/CYA ratio, then you can use a phosphate remover to slow down the algae growth rate.  So the choice is yours -- target a higher FC/CYA level or lower the phosphate level.  Either approach will work.  I wouldn't go lower than around a 3% FC/CYA ratio though.

    At very high phosphate levels combined with high Calcium Hardness (CH) levels then that can cause calcium phosphate scaling in the SWG, but that is uncommon.

  15. Other than exposure to sunlight or using a UV system, the only other way to reduce CC is by water dilution.  Non-chlorine shock might oxidize the CC depending on what it is, but usually non-chlorine shock (potassium monopersulfate) does a better job oxidizing precursors before they form CC.  And MPS shows up as CC unless you use the special reagent that eliminates that interference.

  16. All phenol red tests are not the same because they don't all use the same (or any) chlorine neutralizers in them.  Taylor has the best pH test that contains a proprietary blend of chlorine neutralizers that don't change the pH when neutralizing chlorine up to around 10 ppm FC.  If you use sodium thiosulfate drops to neutralize chlorine, that can raise the pH.  I've compared the Taylor K-2006 phenol red test against a calibrated Oakton pH 5+ and it's right on.

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