chem geek
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Posts posted by chem geek
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Yes, that rule-of-thumb is independent of the spa size because it is the amount of chlorine needed to oxidize bather waste, not the amount needed for a certain FC level (say, for disinfection). It's just a rule-of-thumb and the real amount to add is whatever it takes such that you end up with a small residual (1-2 ppm FC) 24 hours later.
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Follow the Ahh-Some instructions. Generally you do not need to balance the water when using it.
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Yes, MPS is Potassium Monopersulfate but the monopersulfate part of the name has synonyms like peroxymonosulfate or peroxysulfate or the trade name from Dupont for the product called Oxone. When sold as a product, it is really a triple salt of MPS with potassium sulfate and potassium bisulfate. The chemical formula of this triple salt is 2KHSO5•KHSO4•K2SO4 (see Dupont Oxone).
The monopersulfate is an oxidizer where the extra oxygen is in effect in the 0 oxidation state and is sometimes called "active oxygen". This is similar to the extra oxygen in hydrogen peroxide and to organic peroxy acids.
While MPS is a somewhat strong oxidizer, it is a selective one so oxidizes some of the same compounds that chlorine does, such as creatinine, while it does not quickly oxidize others such as ammonia or monochloramine that chlorine more quickly oxidizes. So its use will generally form fewer chlorinated disinfection by-products because it will oxidize some of the bather waste instead of having chlorine do so.
MPS will interfere with chlorine test kits generally registering as Combined Chlorine in DPD tests and as Free Chlorine in FAS-DPD tests (unless the FC is 0 in which case it shows up as CC). There is a Taylor K-2041 MPS interference remover that can be used in Taylor test kits if you are using MPS and chlorine.
You normally do not need to use it if you use chlorine properly and regularly. If you do use it, then it's a supplement to using chlorine. Roughly speaking, with no ozonator, every person-hour of soaking requires around 3-1/2 teaspoons of Dichlor or 3-1/2 fluid ounces of 8.25% bleach or 7 teaspoons of non-chlorine shock (43% MPS) to oxidize bather waste. You do not maintain a constant level -- you do that for chlorine (in between soaks) but for MPS you just use it to help oxidize bather waste after a soak.
There is another use for MPS which is as an actual disinfectant when in the presence of silver ions as in the Nature2 system. In that case, you use MPS alone (with the silver ions from Nature2) though in practice to keep the water clear one usually needs to shock with chlorine every week or two.
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Scrape some off and put it in a ceramic dish or glass cup and add a small amount of acid to it. If it fizzes then it's calcium carbonate (i.e. scale) and one or more of your pH, Total Alkalinity (TA), or Calcium Hardness (CH) are too high. If you are using test strips, they are not generally accurate and you should get a Taylor K-2006 or TF-100 test kit.
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The pool store owner is wrong. You can't even test for Calcium Hardness (CH) with your test strips -- only Total Hardness. Also, test strips are not very accurate particularly for TA, CH and CYA (they can be OK for pH and sometimes FC if done carefully in a controlled environment).
This certainly sounds like calcium carbonate scale though you really need to collect some and add acid to it to see if it fizzes (that would confirm calcium carbonate), but you'll never know until you get yourself a proper test kit, either the Taylor K-2006 or the TF-100.
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How did your CYA jump from 120 ppm to 200 ppm? Obviously the test results you are getting from different pool stores is inconsistent. Also, you should not be using test strips if you want to have accurate readings. Get yourself a Taylor K-2006 or a TF-100 test kit. These are accurate drop-based kits that should give you consistent results.
If your TA is high, that can be lowered with a combination of acid addition and aeration of the water, but if your CH and/or CYA are high, they require water dilution to get lower. It is the combination of pH, CH and TA that are the main factors over-saturating the water with calcium carbonate. While some people do manage their pools with a CH of 1000 by keeping the pH and TA lower, your high CH fill water will increase CH over time with evaporation and refill so you might as well do a partial drain/refill to lower the CH and the CYA.
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I don't know. Assuming you added enough oxidizer after your last soak to handle your bather waste, then if the Spa Frog is working it should maintain the bromine level. You can try bromine tabs in a floater to see if that works and if it does then it's likely the Spa Frog that is the problem.
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The Spa Frog adds bromine to the spa just like a bromine floater would (it does other things as well, but we're talking about the bromine to oxidize bather waste). However, it probably is designed to maintain a background dose of bromine and that is not enough to handle very much bather load. You likely need to add almost as much oxidizer after a soak as you would if you did not have a Spa Frog or a floater. That means roughly 3-1/2 teaspoons of Dichlor or 3-1/2 fluid ounces of 8.25% bleach or 7 teaspoons of non-chlorine shock (43% MPS). 1-2 people for 30 minutes is 0.5 to 1.0 person-hours so would need 3-1/2 to 7 teaspoons of MPS which is roughly 0.8 to 1.6 ounces weight of MPS product. 3 ounces sounds high for each use. However, the REAL rule is to add whatever amount is necessary after a soak such that you maintain a proper residual 24-hours after your soak, so roughly end up at 2-4 ppm Bromine 24-hours later (assuming that's your background bromine level in between soaks when you aren't soaking).
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With bromine you can try and start your soak with a lower level and then add an oxidizer after your soak proportional to your bather load. You would then tune your bromine tab output to be at a lower level you can tolerate for the start of your soak, but that will be roughly 2-4 ppm Bromine you'll need to do to maintain disinfection in between soaks and at that level (which is roughly similar to 1-2 ppm chlorine) you may still notice the bromine too much.
And yes, the Nature2/MPS approach would avoid having any haologen (chlorine or bromine) during your soak though usually with that system you still need to use chlorine once every week or so to keep the water clear. Ozone will not deplete MPS the way it does with chlorine (and as you know ozone will create more bromine from a bromide bank).
As for the saltwater chlorine generator, I think the key is to make sure you maintain CYA in the water, say at 30-40 ppm or so. That will significantly moderate chlorine's strength which will help reduce corrosion rates. The higher salt level does increase corrosion rates, but we haven't heard of any such issues if people also have CYA in the water. With no CYA in the water, the active chlorine level will be high and that may be what the manufacturer is worried about (well, they probably don't understand the FC/CYA relationship).
Using bleach, for every 10 ppm FC you add around 17 ppm salt. One is usually able to go twice as long between water changes compared to the standard WRI formula so this would be a formula of (2/9) x (Spa Size in Gallons) / (# of Person-Hours per Day). If we assume a 350 gallon spa and 7 ppm FC (in 350 gallons) per person-hour needed to oxidize bather waste, then that is 78 days for 1 person-hour per day so at 7 ppm FC/day that's 546 ppm FC which would be around 930 ppm salt. So normally one doesn't get much above 1000 ppm salt when using bleach. Sometimes we hear about 1500 ppm if the water is changed as frequently, but 2000 would be unusual. Also, for a saltwater chlorine generator, the 2000 would be all the time whereas with bleach the average salt level would be even lower than the 1000-1500 peak.
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You understand this correctly. A minimum 7.5% FC/CYA ratio will prevent green and black algae growth regardless of algae nutrient (phosphate, nitrate) level. The Pool Calculator (which is now replaced with PoolMath) does say 1-3 ppm FC with 0 ppm CYA, but that is not because that is the level required to prevent algae growth. It is impractical to be able to maintain only 0.06 ppm FC with no CYA even though that is all that would be needed. With no CYA in the water, chlorine breaks down quickly in sunlight. Also, such low levels of chlorine are not easily measured nor maintained.
I now understand why you were confused. While the calculator used an FC/CYA ratio when CYA is present, it used a practical range when CYA was zero. Sorry for that confusion.
As for the 400 ppm CYA, yes the calculator is just computing a ratio, but it's not very practical to have CYA over 100 ppm since if anything goes wrong and you need to shock the pool with chlorine to get rid of any algae growth, it takes extraordinarily high FC levels to do so. Even the maintenance FC level is impractical. Just because the calculator lets you put in a high CYA level doesn't mean it's a proper thing to do.
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Normally in a spa especially with aeration jets the pH will tend to rise, not fall, unless you are using acidic sources of oxidizer such as non-chlorine shock (potassium monopersulfate, MPS) or a lot of Dichlor.
Of course, it could be your test strips that aren't right though usually pH is reasonably accurate even using test strips.
So what type of chlorine are you using? Chlorinating granules? Does it say "sodium dichloro-s-triazine" or "sodium dichloroisocyanurate" in the ingredients? Are you using any non-chlorine shock (MPS)? You didn't list that. Why did you list "stabilizer"? If you are using Dichlor as your source of chlorine, then you have no need to use stabilizer (Cyanuric Acid, CYA).
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What you are missing is that the equivalent of 0.1 ppm FC with no CYA is more than you need to both kill pathogens and prevent algae growth. The "1-3 ppm FC" you quote is an irrelevant number by itself without saying what the CYA level is. If you have 1-3 ppm FC with no CYA, then that is a HIGH active chlorine level, though is one found in commercial/public pools that don't use CYA such as most indoor pools. This is why such pools oxidize swimsuits, skin and hair faster (my wife has personal experience with this).
You are wrong that most poole including those with high CYA don't have problems. Most do, but not all because some have low algae nutrient (phosphate, nitrate) levels. Between 1/4th and 1/3rd of all pool owners have problems in their pools in the current season while in the past 3 years it's closer to 70-80%. The problems are most commonly cloudy water or visible algae growth or unusual chlorine demand, all of which can occur from algae growth including that which is nascent and not yet visible (cloudy water has other causes, but early algae growth is the most common). On another pool forum website there are over 400,000 visitors PER MONTH during peak summer months because people have problems with their pools. So don't think that people "rarely have an algae problem". It is not rare.
Of course, you may be describing your local experience and as you point out your water may not have phosphates in it. Just note that some municipal water supplies add orthophosphate to the water to prevent metal corrosion. Also, anyone using HEDP-based metal sequestrants will have increasing phosphate levels.
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You are incorrect about the effective or equivalent active level of chlorine. With an FC/CYA ratio of 10%, the active chlorine level is roughly equivalent to only 0.1 ppm FC with no CYA (technically at 77ºF, 40 ppm FC with 400 ppm CYA has the same hypochlorous acid concentration as 0.09 ppm FC with no CYA; at 88ºF it's the same as 0.20 ppm FC with no CYA).
There is a small oxidation effect from chlorine bound to CYA that is no more than 1/150th the rate of that of hypochlorous acid. So perhaps at such higher FC levels the equivalent with no CYA might have as much as 0.5 ppm added to it. This is still lower than commercial/public pools with no CYA in them such as indoor pools. The effects on swimsuits, skin, and hair will be no worse.
Drinking pool water is different since there it is the total capacity of chlorine that would have an effect so the 40 ppm FC would be relevant, but remember that the EPA allows up to 4 ppm FC in drinking water and that assumes drinking around 2 liters or quarts per day for a lifetime and you shouldn't be ingesting very much chlorine.
However, a pool with such a high CYA level is risky in that if algae starts to develop trying to get rid of the algae using chlorine alone will be very difficult since it would take extraordinary FC levels. So it's better to lower the CYA level via water dilution. Usually, those pools won't have 400 ppm CYA because they'll often get algae at their industry-normal FC level of 1-3 ppm unless they are very lucky to have very low algae nutrient (phosphate and nitrate) levels or are using algaecides.
Also, don't forget that CYA contributes to Total Alkalinity (TA) so maintaining water balance to protect plaster pools means having a higher TA level so you have enough carbonate alkalinity.
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Yes, to switch from bromine to chlorine a water change is needed.
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You could use 50 ppm Borates (most easily added using boric acid) to reduce the rate of pH rise. Or you can do as you say and dilute the water to lower the CH to reduce the change of calcium carbonate scaling from high pH.
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The loss of the heater was probably a coincidence since 12 ppm FC is not very high though it partly depends on whether there was any CYA in the water. That is, if you had freshly changed water and used unstabilized chlorine only, such as bleach or lithium hypochlorite, then such chlorine is too strong though even that by itself would cause the heater to fail. If you used Dichlor for your "shock" then that should not have been a problem since the CYA would have moderated the chlorine's strength.
With low CH and a low TA you shouldn't have scaling even with a high pH unless it was VERY high -- much higher than even 8.0.
If you collect some of this rough-feeling stuff and pour some acid on it outside the spa, if it fizzes then it's calcium carbonate scale.
You can calculate dosage using PoolMath. In 330 gallons, for 50 ppm borates you need 19 ounces of 20 Mule Team Borax with 9.3 ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) or about 13 ounce weight (9 fluid ounces volume) of dry acid (93.2% sodium bisulfate). You'd split into at least 3 dose pairs adding acid, then borax, then acid, then borax, etc. making sure it gets mixed each time in the spa water with good circulation.
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Your welcome. It does get easier once you're dialed in and figured out the chlorine demand and other characteristics of your spa.
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The main reason to use 120-150 ppm CH in a spa is to help prevent foaming. If you do not have a foaming problem then you don't need to raise the CH.
You need to be more aggressive with lowering your TA by following the procedure of aerating at low pH and adding acid. See Lowering Total Alkalinity.
50 grams of Dichlor in 330 gallons would increase the CYA by 20 ppm.
If you have never used Ahh-Some I suggest you do so. Both the new spa as well as the period of time with no chlorine could create biofilms and those are difficult to remove with chlorine alone (though superchlorating can help, the use of Ahh-Some is more effective for their removal).
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So the higher CYA level would slow down the rate of chlorine oxidizing the bather waste. With your now lower CYA the chlorine should react more quickly.
A low CSI in an acrylic spa is not a problem so long as your pH doesn't get low. A balanced CSI is for protecting plaster surfaces. Metal corrosion has more to do with low pH and strong oxidizers than with CSI. See the discussion in this link.
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Yes, if you remove the feeder the level should drop. Also, your use of Replenish also increases the bromine level. So if you stop both, you should see the level drop and then just add enough Replenish after a soak OR use the floater dialed down to maintain the proper bromine level.
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Those test strips are fine for measuring the salt level. They will not distinguish between chloride vs. bromide salts, but that shouldn't matter. You can use the strips you have for determining the salt level for your generator, though adding the proper amount of salt to the water should be sufficient since tap water has little salt in it.
If you were to get the Taylor K-1766 kit it is a drop-based test, but these salt tests actually measure the chloride concentration since the precipitate silver chloride, though they report their units as ppm sodium chloride. That's standard and not a problem.
With a saltwater chlorine generator you do not need to build a free chlorine reserve as it will generate chlorine. The reason you want to use some stabilized chlorine is to build up some Cyanuric Acid (CYA aka stabilizer or conditioner) to the water so that the chlorine is not too strong/harsh. You could add pure CYA directly, but it dissolves slowly while Dichlor dissolves quickly.
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Yes, you can move to bleach since your CYA isn't terribly high. Remember that most people use Dichlor-only which keeps building up the CYA level higher and higher, though after it gets over 100 or 200 ppm that's when we've seen more reports of hot tub itch/rash/lung.
You don't change the per person-hour formula. That's the amount of oxidizer needed to oxidize bather waste and is independent of the CYA level. The higher CYA will make that process slower so if you were to soak frequently back-to-back such as twice a day you may get behind or if you soak every day with high bather loads you may get behind (i.e. have a buildup of bather waste yet to be oxidized and perhaps also a buildup of combined chlorine).
Worst case, if you find you aren't able to oxidize the bather waste quickly enough, you can do a partial drain/refill to get the CYA lower, but I think you'll be OK with where you are at. Certainly you can try it out first.
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Are your test strips like these from Aquachek? If so, then they measure sodium chloride salt, NOT sodium alone. The Taylor drop-based salt test measures chloride (it titrates silver chloride).
Yes, your saltwater chlorine generator is for chlorine and expects chloride in the water. Your dealer gave you the wrong salt to use. You need to drain and refill because the bromide in your water will make bromine, not chlorine (the saltwater generator may make chlorine but then the chlorine will react with bromide to make bromine).
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Add the acid slowly with the circulation pump running (preferably add it over a return flow) and you should be OK. You can lightly brush the sides and bottom in the area where you add the acid to ensure thorough mixing.
You should consider getting an automated acid dosing system using a peristaltic pump as that can inject acid into the circulation system very slowly so as not to crash the pH.
Noob Water Chemistry
in Portable Hot Tubs & Spas
Posted
pH Up (soda ash) would increase both pH and TA. If the TA still needs to be raised further when the pH is OK, use baking soda (or pay more for Alkalinity Up at your spa or pool store). By "CA" do you mean "CH" or Calcium Hardness (as opposed to CYA or Cyanuric Acid)?
Are you sure CC is 1.5 ppm? Or is that Total Chlorine so CC is really 0.5 ppm? Are these readings from the dealer or from your own good test kit such as the Taylor K-2006 or for bromine the K-2106 (though you can use the K-2006 for both).
To get to a pH of 7.5 with your numbers you'd add only 0.8 ounces weight or only 1/10th cup of soda ash. That should bring the TA up to around 52 ppm as well. You can then add 1.5 ounces weight (1.2 fluid ounces volume) to get the TA to 70 ppm since I presume using bromine you may be using some net acidic chemicals. There's no way you add 3/4 cup -- where are you getting such quantities?
To preven foaming, you could increase calcium hardness, but you could just wait to see if foaming is a problem in your spa.
Dichlor-then-bleach wouldn't necessarily be any easier on startup given the water parameters you have.