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chem geek

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About chem geek

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    Wizard of Water

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    San Rafael, CA
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    Interested in pool water chemistry. Undergrad degree in physics/chemistry. MBA. Other interests include swimming, skiing, genealogy.
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  1. I sure do wish you would come back and post on the forum, because your posts have taught me quite about about water chemistry. I can imagine that it would grow tiresome to continue answering the same questions over and over; however, there are plenty of us with new, unique questions who sure could use your help!

  2. 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 sodi
  3. 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 or
  4. 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,
  5. 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 i
  6. 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 p
  7. 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 sticki
  8. 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 equivalen
  9. 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.
  10. 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
  11. 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
  12. 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).
  13. You only need the CH higher in a spa if you have a plaster surface or to reduce foaming, but the ACE system requires low CH levels usually 50 ppm or lower and they have a calcium remover pouch to lower the CH. So for ACE you should not try raising the CH. If your spa is not plaster (most are acrylic instead) then you don't need to worry about the low CH.
  14. Roughly 3-1/2 fluid ounces of 8.25% bleach per person-hour, but again this is a rough guideline. You should add enough oxidizer after your soak so that you still measure some (1-2 ppm FC) chlorine residual before your next soak.
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