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Thread: Spa plaster flaking

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    Spa plaster flaking

    Split from spa-plaster-flaking-t18261.html Butterfly


    Quote Originally Posted by Centers*for*Disease*Control*and*Prevention
    A high TDS level can mean a high organic contamination level. The TDS level should never increase more than 1,500 parts per million higher than the startup level of the pool.


    Is there a pool website in business anywhere on the net that doesn't gently or forcefully admonish pool owners to guard against the evils of excessive TDS? Beware its intents and know the consequences.... It's fairly persuasive: Isn't very high TDS a contributor to poor sanitation, as an agent in either the inhibition of chlorine or in its destruction (I've read both claims)? Isn't it somehow disruptive to pH and the ability to balance the water? Doesn't it lead to problems in the effective control of algae? Harbor pathogens? Responsible for cloudy water, red eyes, premature equipment failure... and delirium (an understandable response when facing an enemy so ill-defined as to be both invisible and invincible.) It seems to require the promiscuous use of one's mental faculties to resist what may well be a blunderous fallacy, however benign.

    Scott has identified the crux of this misapprehension in that the "relatively inexperienced" (I'm a card-carrying member) are prone to assembling a solid, working misunderstanding of problems they have faced and licked – success come, perhaps, by way of the underrated virtue of doing nothing (to make the problem worse!) Or the passage of time.

    If there’s some confusion about causality it should be forgiven us neophytes who, after all, are just grasping at straws—doing the best we can do with limited information. But I find it puzzling that a goodly number of pool professionals are seemingly in league with the water diviners and civil engineers, the recreational water experts, the industry pitchmen, even the dry chemists*, testing labs and aquatics facilities in propagating what most here believe is baseless.

    * Special contributors to this forum, graciously excluded.
    14,555 gal in-ground 16'x29' white plaster Pool w/spa (2007); Goldline Aqua Logic AQL-PS-8 control w/Aqua Cell 15 Salt Water Chlorination (SWCG); Hayward TriStar 1HP (1.85 SF) main / 1.5HP (1.60 SF) spa pumps; Hayward Swimclear cart filter C4025, ColorLogic LED lights; Tankless SP-18-4 electric heater; Polaris 280 cleaner.
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    Re: Spa plaster flaking

    I just stumbled onto this topic and had to reply. The ScaleTec will work on the white flakes coming from your heat exchanger it just takes time. You may also want to look at Beautec as a preventive as well. Not as to address the old water issue. For some reason I see and hear this topic alot. And for some reason no one every thinks about TDS. I will be quoting from and artilce. But this is some thing that a normal testing station will not test for.

    "TDS - Total Dissolved Solids - may be the most misunderstood factor in the whole field of pool & spa water chemistry. It's misunderstood because no one knows exactly what effect it is going to have on any particular body of water.

    When everything else seems to be all right, and the water still acts screwy, check the TDS.

    High TDS can result in corrosion of metal equipment and accessories, even though the water is balanced.
    High TDS can cause eye and skin irritation, even though the pH is right and there are no chloramines in the water.
    High TDS can permit an algae bloom, even with a 2-3 ppm chlorine residual.
    But none of these symptoms will necessarily occur. It is the uncertain nature of problems caused by TDS that makes it such a headache to deal with.

    As its name states, TDS is the sum total of all of the dissolved things in a given body of water. It's everything in the water that's not actually water. It includes hardness, alkalinity, cyanuric acid, chlorides, bromides, sulfates, silicates, and all manner of organic compounds.

    Every time you add anything to the water, you are increasing its TDS. This includes not only sanitizing and pH adjusting chemicals, but also conditioner, algaecides, and tile and surface cleaners. It includes airborne pollutants and bather waste as well as dissolved minerals in the fill water.

    At low levels, TDS does not present a problem. In fact, a certain amount of TDS is necessary for water balance. Hardness and Total Alkalinity are both part of TDS.

    But at high levels - above 3,000 parts per million - you are welcoming problems. The National Spa & Pool Institute, in its standards for both swimming pools and spas, recommends an ideal TDS of between 1,000 and 2,000 ppm, with a maximum of 3,000 ppm.

    No one knows exactly what mechanism is at work when you're dealing with high TDS water. One commonly held theory is that when you get a lot of dissolved substances in water, they interfere with the normal workings of sanitizers. They may do this by forming a chemical "shield" around bacteria, algae, and other substances normally attacked by chlorine or bromine. Or they may simply present "roadblocks" in the path of sanitizer molecules, preventing them from freely circulating.

    TDS buildup is inevitable. As we've explained, every time you add chemicals to water, you're increasing the TDS. When the water evaporates, it leaves behind all of the solids that had been dissolved in it.

    Just how much are you increasing the TDS when you chemically treat pool or spa water? Well, for every pound of dry chemical that you add to a 15,000 gallon pool, you are increasing the TDS by about 8 ppm.

    "Parts Per Million" is what scientists refer to as a "weight to weight" measurement. That is, if you know how much the water weighs, and you know how much the stuff you are adding to the water weighs, you can calculate how many parts per million you are adding to the water.

    As it happens, one gallon of water weighs 8.34 pounds. So if you know how many gallons are in a pool or spa, and you multiply that number by 8.34, you will know how many pounds of water are in the pool or spa.

    So, how many pounds of water are in a 450 gallon spa? The answer is 3,753 pounds (450 x 8.34 = 3,753). How about a 15,000 gallon pool? Well, 15,000 x 8.34 = 125,100. So, there are 125,100 pounds of water in a 15,000 gallon pool.

    OK, so now you know how much the water weighs. Now, take 1 million and divide it by the total weight of that water, and you will find out how many parts per million are contained in each pound of water. For example, 1,000,000/125,100 (pounds of water in our 15,000 gallon pool) = 7.99. We'll call it 8. That is, every pound of material added to a 15,000 gallon pool will contribute about 8 parts per million.

    How about our 450 gallon spa? Take 1,000,000, divide it by 3,753 (the weight of the water in the spa), and you get 266.45. We'll settle on 266. So for every pound of stuff that you add to a 450 gallon spa, you will be increasing the TDS by 266 parts per million.

    Incidentally, if you wanted to design a pool that would contain almost exactly 1 million pounds of water, it would be a 120,000 gallon vessel. In that pool, every 1 pound of solids dissolved in the water would increase the TDS by 1 ppm.

    Every sanitizing chemical, and every pH adjusting chemical used in the pool and spa industry will eventually contribute to the TDS in a pool or spa. Some will contribute more than others. Because sanitizing compounds often require the additional use of pH adjusting chemicals, the chemical maintenance regimen you choose can have a dramatic effect on the buildup of TDS.

    TDS is fairly easy to calculate for dry chemicals. It's a bit more complicated for liquid solutions. If a research lab were going to test the solids content of a liquid, they would take a precise volume of the liquid and then slowly heat it until the liquid itself had evaporated. Then they would dry the remaining solids and weight them.

    The two most common liquid solutions used in our industry are muriatic acid and liquid chlorine (sodium hypochlorite). For your information, 1 gallon of muriatic acid will contribute 1.87 pounds of dissolved solids to the water. 1 gallon of liquid chlorine will contribute 2.2 pounds of dissolved solids.

    You should also understand that every type of chlorine & sanitizer - including gas chlorine - eventually ends up contributing to TDS in the form of chloride. So every time you add a pound of dry chlorine compound, or infuse a pound of gas chlorine into a 15,000 gallon pool, you will wind up increasing the TDS by about 8 ppm.



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    Another Article
    Total Dissolved Solids (TDS) are the total amount of mobile charged ions, including minerals, salts or metals dissolved in a given volume of water, expressed in units of mg per unit volume of water (mg/L), also referred to as parts per million (ppm). TDS is directly related to the purity of water and the quality of water purification systems and affects everything that consumes, lives in, or uses water, whether organic or inorganic, whether for better or for worse.

    What Are Total Dissolved Solids?

    "Dissolved solids" refer to any minerals, salts, metals, cations or anions dissolved in water. This includes anything present in water other than the pure water (H20) molecule and suspended solids. (Suspended solids are any particles/substances that are neither dissolved nor settled in the water, such as wood pulp.)

    In general, the total dissolved solids concentration is the sum of the cations (positively charged) and anions (negatively charged) ions in the water.

    Parts per Million (ppm) is the weight-to-weight ratio of any ion to water.

    TDS is based on the electrical conductivity (EC) of water. Pure H20 has virtually zero conductivity. Conductivity is usually about 100 times the total cations or anions expressed as equivalents. TDS is calculated by converting the EC by a factor of 0.5 to 1.0 times the EC, depending upon the levels. Typically, the higher the level of EC, the higher the conversion factor to determine the TDS.
    Where do Dissolved Solids come from?

    Some dissolved solids come from organic sources such as leaves, silt, plankton, and industrial waste and sewage. Other sources come from runoff from urban areas, road salts used on street during the winter, and fertilizers and pesticides used on lawns and farms.

    Dissolved solids also come from inorganic materials such as rocks and air that may contain calcium bicarbonate, nitrogen, iron phosphorous, sulfur, and other minerals. Many of these materials form salts, which are compounds that contain both a metal and a nonmetal. Salts usually dissolve in water forming ions. Ions are particles that have a positive or negative charge.

    Water may also pick up metals such as lead or copper as they travel through pipes used to distribute water to consumers.

    Note that the efficacy of water purifications systems in removing total dissolved solids will be reduced over time, so it is highly recommended to monitor the quality of a filter or membrane and replace them when required.
    Why Should You Measure the TDS level in your Water?

    The EPA Secondary Regulations advise a maximum contamination level(MCL) of 500mg/liter (500 parts per million (ppm)) for TDS. Numerous water supplies exceed this level. When TDS levels exceed 1000mg/L it is generally considered unfit for human consumption. A high level of TDS is an indicator of potential concerns, and warrants further investigation. Most often, high levels of TDS are caused by the presence of potassium, chlorides and sodium. These ions have little or no short-term effects, but toxic ions (lead arsenic, cadmium, nitrate and others) may also be dissolved in the water.

    Even the best water purification systems on the market require monitoring for TDS to ensure the filters and/or membranes are effectively removing unwanted particles and bacteria from your water.

    The following are reasons why it is helpful to constantly test for TDS:

    How do you reduce or remove the TDS in your water?

    Common water filter and water purification systems:


    1. Carbon Filtration
    Charcoal, a form of carbon with a high surface area, adsorbs (or sticks to) many compounds, including some toxic compounds. Water is passed through activated charcoal to remove such contaminants.
    2. Reverse Osmosis (R.O.) Reverse osmosis works by forcing water under great pressure against a semi-permeable membrane that allows water molecules to pass through while excluding most contaminants. RO is the most thorough method of large-scale water purification available.


    3. Distillation
    Distillation involves boiling the water to produce water vapor. The water vapor then rises to a cooled surface where it can condense back into a liquid and be collected. Because the dissolved solids are not normally vaporized, they remain in the boiling solution.


    4. Deionization (DI)
    Water is passed between a positive electrode and a negative electrode. Ion selective membranes allow the positive ions to separate from the water toward the negative electrode and the negative ions toward the positive electrode. High purity de-ionized water results. The water is usually passed through a reverse osmosis unit first to remove nonionic organic contaminants.





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    TDS Testing
    Short of a detailed laboratory analysis, the most dependable method of TDS testing is through the use of a portable TDS meter. These meters actually measure the conductivity of the water - its ability to conduct an electrical charge, which happens to increase as the TDS increases.

    Hand-held TDS meters - usually in the $50.00 - $150.00 range, generally operate by either placing some water in a sample cell or dipping the meter directly into the pool water and pushing a button, which causes a small electric current to pass between two electrodes immersed in the water and separated by a specific distance.

    The meter measures the current passing between the electrodes and uses that to determine the water's conductivity The meter dial (or LCD readout) is calibrated to indicate TDS in parts per million.

    The easiest way to reduce TDS is to drain and refill it with fresh water. This can also be done in stages, taking the water level down 1 or 2 feet at a time and refilling over a period of days or weeks.

    Under normal circumstances, pool water can be expected to last anywhere from 3 to 5 years before it has to be completely changed. Your choice of chemical treatment can help to determine just how long it lasts."

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    Re: Spa plaster flaking

    TDS is irrelevent. The reason why algea grows at "even 2-3 ppm chlorine" is most likely because the CYA level is so high that 2-3 ppm is ineffective. At 30 -40 ppm CYA, the target level for chlorine is 4-5 ppm. If pucks are used, as they are in a lot of residential pools, the cya level can be well over 100 ppm. again, the reason for algea in a pool is inadequate chlorine levels.
    These articles contain dubious material at best and in some cases or plain wrong.
    Calling chemgeek!!!
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    Re: Spa plaster flaking

    There are multiple reasons for algae growth in a pool. CYA levels too high is not an accurate statement. With Cya too high you either lock in Chlorine or you Lock it out. If you have high levels of CYA and you still have a Free Chlorine level of 1 or higher algae will not form unless you have another problem. Make sure you are testing for FREE CHLORINE and not TOTAL CHlORINE. When you are trying to see if you have a proper chlorine level in your pool.

    Lack of free chlorine is another reason for algae grow

    Example would be If you have a FC level of 1.0 and you have TC level of 2.0. You need to shock your pool. With more than a .3 differential between your FC and Your TC. You are experiencing high levels of chloramines. Chloromines are what cause the pungent smell of chlorine at a pool or spa. And are also responsible for irritaion of the eyes in a pool(MOst of the time) not the chlorine itself.


    High Phosphate levels can also cause an algae bloom.
    Normally When you have this problem you will also have a problem keeping chlorine in the pool no matter how many times you shock the pool.

    And yes high levels of TDS can and will cause an algae issue if not addressed.

    The information that I provided earlier comes from a water testing facility not myself.

    Hope this helps,

    David

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    Re: Spa plaster flaking

    I have a great deal of interest in this discussion and would like to see it continue but I shouldn't have been so provocative at the expense of another member's issue.

    Can a moderator or admin prune the discussion from this thread beginning with my earlier post and put it some place more appropriate? Thanks! And sorry again for the hijack.
    14,555 gal in-ground 16'x29' white plaster Pool w/spa (2007); Goldline Aqua Logic AQL-PS-8 control w/Aqua Cell 15 Salt Water Chlorination (SWCG); Hayward TriStar 1HP (1.85 SF) main / 1.5HP (1.60 SF) spa pumps; Hayward Swimclear cart filter C4025, ColorLogic LED lights; Tankless SP-18-4 electric heater; Polaris 280 cleaner.
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    Re: Spa plaster flaking

    Quote Originally Posted by fighting_irish

    With Cya too high you either lock in Chlorine or you Lock it out. If you have high levels of CYA and you still have a Free Chlorine level of 1 or higher algae will not form unless you have another problem.
    Patently false. At high CYA levels, it takes more free chlorine to over come the high stabilizer levels. This chart shows the relationship here:

    pool-school/chlorine_cya_chart_shock

    There is really no such thing as chlorine lock as clasically described by the industry. If you add enough free chlorine to over come the CYA levels in a particular pool, and/or have little or no combined chlorine, you will have enough FC to defeat algea. The idea of chlorine " lock" is not really true.

    Quote Originally Posted by fighting_irish

    Example would be If you have a FC level of 1.0 and you have TC level of 2.0. You need to shock your pool.
    At an FC level of 1, there is not enough FC to keep algea out of you pool even at 20 ppm CYA.


    Quote Originally Posted by fighting_irish
    High Phosphate levels can also cause an algae bloom.
    Also false. Phosphate levels are not relevent if you keep the FC in your pool in adequate amounts relative to the stabilizer levels as shown above.

    Quote Originally Posted by fighting_irish
    And yes high levels of TDS can and will cause an algae issue if not addressed.
    What is the basis for this statement?

    High levels of CYA will cause chlorine to be less effective at lower FC levels. Increased levels of CYA need more FC. Higher levels of calcium can casue scaling, especially at higher pH values. Partial drains and refills are required to address the issue. But, TDS levels in general are not a concern if the water is balanced properly. Testing of the water and the knowledge about what to do with the results is the key to keeping a pool happy.

    Again, high TDS in and of itself is not an issue.
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    Re: Spa plaster flaking

    Quote Originally Posted by polyvue
    I have a great deal of interest in this discussion and would like to see it continue but I shouldn't have been so provocative at the expense of another member's issue.

    Can a moderator or admin prune the discussion from this thread beginning with my earlier post and put it some place more appropriate? Thanks! And sorry again for the hijack.
    Maybe we move it to the deep end?
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

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    Re: Spa plaster flaking

    My apologies to the OP. If my statements have come off invalid to the topic at hand.

    Thanks,

    David

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    Re: Spa plaster flaking

    Its just that the OP was talking about flaking in his pool and the topic veered off into TDS, thats all.
    On this forum, folks are not big believers in high TDS levels being bad per se. Properly balanced water, no matter what the over all TDS level is, is all one needs for a happy pool. Just because the over all TDS level is high, doesnt mean there is a problem with the pool. Individual constituents in the water such as calcium, CYA, CC, TC etc, all contribute to potential problems if they are too high or too low. As i said earlier, proper testing of the water and knowing what to do with the results will result in a much easier pool to take care of. Following industry lore and, honestly, false information, (i.e chlorine lock, phosphates are bad, high TDS is bad, CYA levels do not matter, etc) will result in headaches, un-needed expense and hassle. People on this forum have found that a lot of information that is touted is designed in part, to sell expensive chemicals and to sell a "magic pill" to take care of a pool when in reality, proper water testing, and some basic chemicals from the grocery store and walmart will keep a pool very happy for not a lot of dough.
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    Re: Spa plaster flaking.... TDS?

    Quote Originally Posted by fighting_irish
    I just stumbled onto this topic and had to reply.
    ... And reply you did! Thanks for posting the articles. There's a real debate here and one that may not be resolved any time soon but you might want to entertain the notion -- if only as a thought experiment -- that there is at least a metaphysical possibility that the conventional wisdom as conveyed by a legion of industry professionals and others is... dead wrong.

    I'm glad you felt the need to respond because it showed you understood what I was saying: There is definitely a disconnect between much of what I've read, and you've excerpted, from industry periodicals and related publications on topics like TDS that are not accepted by many people on this forum. Why do you suppose that is the case? If you find this difficult then you also know how it must be for some here to have had the benefit of training, acquired knowledge or experience on a subject but find that their hard-won education in working out these reasonable truths is not well respected outside a limited sphere of influence. Depending on your perspective, you're either a flat-earther and the world knows only circles or you have the requisite understanding that the world is a pear-shaped sphere but your friends and colleagues regard your theories as quackery, because everyone knows the world is exactly 1 millimeter thick and they have 16 concurring studies (printed on incredibly thin wafers) to prove it.

    The articles excerpted in your post, though without references, are quite familiar to me. A little googling would likely produce the whole lot in a few seconds, and an untold number of copies that have been cut & pasted into the Water Chemistry sections of a thousand pool sites. I found my lips moving as I read through them – and not just because I’m a little slow in the thought production division.

    I know the intent behind some of these articles is prescriptive or didactic – it’s meant to help people understand a concept, acquire a skill or accomplish a task. For that reason, there isn’t a whole lot to chew on for me. I don’t think most folks here have a sustained interest in chemistry; however we want to understand as much as possible about the underlying processes, to evaluate competing claims and to determine for ourselves whether the procedures we’ve been taught hold water (sorry, couldn’t resist). It’s great to have assertions and it’s an unfailingly good place to start— but there may be more and different or better truths.

    Quote Originally Posted by fighting_irish
    My apologies to the OP. If my statements have come off invalid to the topic at hand.
    No, no. You had the decency and thoughtfulness to actually provide some advice to the OP -- I forgot the advice and starting riffing on a favorite subject.
    14,555 gal in-ground 16'x29' white plaster Pool w/spa (2007); Goldline Aqua Logic AQL-PS-8 control w/Aqua Cell 15 Salt Water Chlorination (SWCG); Hayward TriStar 1HP (1.85 SF) main / 1.5HP (1.60 SF) spa pumps; Hayward Swimclear cart filter C4025, ColorLogic LED lights; Tankless SP-18-4 electric heater; Polaris 280 cleaner.
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    Re: Spa plaster flaking

    TDS is almost completely meaningless for swimming pools. Knowing the total doesn't help at all. What is important is knowing the levels of the individual chemicals and checking to see if any of the important chemical levels are too high. For example several thousand ppm of salt does not cause any problem, while several hundred ppm of CYA could easily cause significant problems.

    Ocean water pools have TDS levels in excess of 30,000 and yet they are no more prone to problems than other pools with far far lower TDS levels. At the same time, it is quite possible to have serious problems with TDS levels under 1,000. If you know exactly what chemical treatment regime has been used, TDS could be used to guess at some of the other levels. But since all of the actually important levels have individual test available these days, it is far simpler and more reliable to do the individual tests, and ignore TDS.

    The pool industry has a long history and advice from long long ago is often repeated even though it no longer applies. TDS used to be used as a proxy for CYA levels back before CYA tests were commonly available. When chemicals were added according to the practices common at that time, TDS levels would rise at about the same rate as CYA levels. Thus, high TDS levels were very suggestive of high CYA levels. If you don't have a CYA test, that becomes important even if the correlation was not completely reliable.

    These days we do have CYA tests, and can find out if we have a CYA problem for sure by measure the CYA level directly. The most common ways chemicals are used has also changed, leading to many more situations where TDS is high and yet there is not a problem. For example, significant amounts of salt are frequently added to swimming pools these days, while that was extremely rare 50 years ago. Thus modern TDS levels are far higher than they were when the TDS "rules" were originally invented.

    The pool industry is full of advice like this, which has outlived it's usefulness. There is also a fairly large amount of advice given that is just plain wrong. Pool stores have strong financial incentives to give incorrect advice. As long as you are having problems, you will keep going to the store and spending more money. Many stores give good advice none the less, but the temptation is always there and enough of them fall prey to it to cause problems.

    If all of that wasn't enough of a problem, advice often changes over time, as it is passed from person to person. Over time, originally sensible advice can lose both the original context and intention and becoming completely divorced from reality. Further, the chemistry behind swimming pools is quite complex. It is always "dumbed down" to some extent so that people without advanced chemistry degrees can understand it. Unfortunately, that opens the door to misinterpretations. Many people are quick to "reason" on the basis of misleading simplified rules and draw completely incorrect conclusions because they don't understand the principals behind the original rules.

    Because of all of this, we get lots of material, like what fighting_irish quoted above, that is full of a mixture of good information and bad information. There are so many mistakes in the material quoted by fighting_irish, that I hesitate to even try to start refuting them. All of those points have been covered several times around here. Most of them are addressed in Pool School.
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    Re: Spa plaster flaking

    Jason's explanation is excellent. Let me give a few examples that demonstrate the absurdity of looking at TDS as well as some cases where it isn't completely ridiculous.

    Low Bather Load Pool
    Take an extreme example where you are adding bleach or chlorinating liquid to an outside pool exposed to sunlight, but where the bather load is low or even zero and there are no leaves, pollen, etc. getting into the pool. At a 2 ppm FC per day chlorine usage from breakdown by sunlight, the salt level from the chlorine will rise by almost 600 ppm in 6 months. If there is no dilution of the water, then this is a rise of 3000 ppm salt in 5 seasons (assuming a 6-month swim season and no chlorine usage in the off-season). This rise in salt directly contributes to the same increase in TDS. Yet obviously there was nothing wrong with the water getting passed 2000 ppm which is 1500 ppm higher than the starting TDS which is usually around 500 ppm at normal CH and TA levels. There may be minimal organics getting into the water.

    Many residential pools have low bather load so that the rise in TDS does not really represent an increase in organics. Note that the CDC wording said "A high TDS level can mean a high organic contamination level" where I have emphasized the word "can". In fact, many organics are neutral (though possibly polar and soluable) compounds that would not increase the conductivity of the water and therefore not get measured as TDS in conductivity tests anyway.

    Saltwater Chlorine Generator (SWG) Pool
    An SWG already starts out with added salt, usually to 3000 ppm which results in a typical initial TDS of 3200 ppm (due to calcium and bicarbonate). However, any chlorine generated comes from chloride in the water so when that chlorine gets used up it becomes chloride again. Therefore, without dilution, the salt level doesn't change. In practice, in pools with rising pH, acid is added as well as baking soda (over time) so that salt levels can rise (or with sufficient dilution, they can fall), but in a pool balanced to minimize pH rise this is a small effect. So in an SWG pool, you won't see a 1500 ppm rise in TDS from bather load and therefore can't really use it as a proxy for organics in the water or if you do.

    High Bather Load Pool
    In many commercial and public pools, the bather load is so high that most of the chlorine demand is from the bather load and not from breakdown by sunlight. It is this scenario where the increase in TDS, which is almost all an increase in salt from the chlorine, can be a rough proxy for unoxidized organics though obviously the kind of chlorine used will have a large effect since bleach and chlorinating liquid result in twice as much salt (and TDS) increase as chlorine gas, stabilized chlorine, and (roughly) Cal-Hypo.

    Water dilution is a good thing, but dilution that keeps the salt level from chlorine usage in check also dilutes other chemicals including organics as well. A rough rule for dilution of pool water in the ANSI/APSP-11 guidelines is replacement of 7 gallons of water per bather (with some presumed, but unspecified, amount of swim time). This is an extraordinary amount of dilution that would keep all chemical levels, including salt (and TDS), from rising when the bather loads are high.

    Conductivity and Corrosion
    Most TDS tests are done by measuring conductivity (another method boils or evaporates the water and weighs the resulting solids; another method is an acid-base titration using an ion exchange resin). Higher conductivity of the water increases the metal corrosion rate, though the rate is low for most pool materials since they do not generally include simple iron or zinc. There is also an increase in stainless steel corrosion when the chloride level gets high (especially when sulfate levels are also higher). However, a chloride test for salt would tell you whether the conductivity is too high and probably be more accurate than typical TDS tests.

    Algae
    In addition to organics, both phosphates and nitrates can accumulate and these accelerate algae growth (up to a point), BUT a proper FC/CYA ratio will prevent such algae growth in spite of these increased nutrient levels. In pools that use stabilized chlorine or otherwise have low active chlorine levels, it may seem that higher TDS results in algae, but it is insufficient active chlorine levels often due to higher CYA that are to blame.


    So while rising TDS, which is really rising salt levels, in high bather load pools can be a reminder to perform required water dilution, it is not a useful or practical measurement for residential pools except to detect very high conductivity levels (in which case a simple chloride salt test could do the same).

    Richard
    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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    duraleigh's Avatar
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    Apr 2007
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    Re: Spa plaster flaking

    In addition to the two very explanatory posts by Richard and Jason there is another factor we shouldn't overlook.

    For over 10 years, people on this forum and the old PF have been successfully maintaining a wide variety of pools for a long period of time with virtually no thought given to TDS. Simply put, ignoring TDS works. For the vast majority of us, (outside the deep end) that's reason enough.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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