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Thread: Should TDS be part of the 'PoolMath' ?

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    Should TDS be part of the 'PoolMath' ?

    I may be picking at a non-issue....but should TDS (Total Dissolved Solids) be considered into PoolMath?

    Does it matter if one has TDS that are unknown?

    Should one be checking TDS?

    Thanks to TFP, I no longer take water samples to the pool store, but when I did they always had a printout showing TDS, I never paid any attention to it and no one ever mentioned to me if it was high or low or whatever.
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    Re: Should TDS be part of the 'PoolMath' ?

    TDS is used in the background of PoolMath to modify certain calculations. But in general TDS is unimportant. Pool Stores test for it as a way of scaring people into buying things they don't need.


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    Re: Should TDS be part of the 'PoolMath' ?

    TDS is used as part of the formula for the Calcium Saturation Index (CSI), but as i've learned here is not relevant as a measurement as far as adjusting pool chemistry. It is more important what the TDS is composed of, e.g. CYA, salt etc. A saltwater pool will have TDS of 3000-4000 just from the sodium chloride alone, so the number is meaningless as a diagnostic tool
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    Re: Should TDS be part of the 'PoolMath' ?

    Exactly, in actuality, it's meaningless in terms of importance to pool chemistry. I record mine once every two or three months just for a view of the big picture, but don't do anything about it, because you can't save by water replacement or mechanical purification.
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    Re: Should TDS be part of the 'PoolMath' ?

    Quote Originally Posted by poolnoob.ca View Post
    TDS is used as part of the formula for the Calcium Saturation Index (CSI), but as i've learned here is not relevant as a measurement as far as adjusting pool chemistry. It is more important what the TDS is composed of, e.g. CYA, salt etc. A saltwater pool will have TDS of 3000-4000 just from the sodium chloride alone, so the number is meaningless as a diagnostic tool
    It is not true that CSI is not important. There is a vast over-simplification and squeezing of ranges in the Recommended Levels in the Pool School in an attempt to simplify for newbies so that they don't have to look at the CSI. Hence "just stay within Recommended Levels" as the usual response. However, if one were to go to the low-end vs. high-end of those Recommended Levels, then one can swing in CSI. The swings would likely not cause scaling, but it all depends on details. In a hot spa, for example, scaling has been seen as low as +0.3 compared to pools where it's usually not seen until +0.7 or higher. Also, the Recommended Levels for SWG pools at the low-end get dangerously low for dissolving of plaster to -0.56 (see this recent post) which means the pool water only has 28% of the needed amount for calcium carbonate saturation. CSI is a logarithmic scale so even -0.3 means the water only has 50% of the needed amount for calcium carbonate saturation.

    TDS IS part of PoolMath. It is automatically calculated internally from the Salt level and the TA and CH levels. It even has a minimum assumption based on TA and CH given that the CH in many pools is added by calcium chloride so increases chloride salt levels. This is all then automatically fed into the Calcite Saturation Index (CSI) calculation.
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    Should TDS be part of the 'PoolMath' ?

    Chemgeek, this may be off topic for this thread, but it goes with the topic of your post. I've started a new thread, for my related question.


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    Re: Should TDS be part of the 'PoolMath' ?

    Quote Originally Posted by poolnoob.ca View Post
    TDS is used as part of the formula for the Calcium Saturation Index (CSI), but as i've learned here is not relevant as a measurement as far as adjusting pool chemistry. It is more important what the TDS is composed of, e.g. CYA, salt etc. A saltwater pool will have TDS of 3000-4000 just from the sodium chloride alone, so the number is meaningless as a diagnostic tool
    @chemgeek, that's what i said, that TDS is not relevant, i didn't mean that CSI is not relevant, of course it is
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    Re: Should TDS be part of the 'PoolMath' ?

    Quote Originally Posted by chem geek View Post

    TDS IS part of PoolMath. It is automatically calculated internally from the Salt level and the TA and CH levels. It even has a minimum assumption based on TA and CH given that the CH in many pools is added by calcium chloride so increases chloride salt levels. This is all then automatically fed into the Calcite Saturation Index (CSI) calculation.
    Even without a SWG, I should at least check my salt level (have been guessing based on chlorine used) and if the minimum assumption is that I added calcium chloride the PoolMath may be a tad off for myself.
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    Re: Should TDS be part of the 'PoolMath' ?

    I haven't got a clue what my TDS is. It's never been tested in at least five years that I know of. Never mind that it's never gone green in thar whole time, never had complaints about skin or eye irritation, never smelled like a hotel hot tub...what if my TDS is high? I'll have to drain!!!
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    Re: Should TDS be part of the 'PoolMath' ?

    Chem geek and I disagree on the importance of csi. I simply cannot argue the technical merits but, from a practical standpoint, I can say that thousands upon thousand upon thousands of pools stay swimmable and crystal clear and do not have calcium scale issues and their pool water managers NEVER calculate csi.

    I do not have the background to understand it's precise importance but I know for the large majority of us, we do not need to be concerned with csi as long as the parameters we test for are kept within the ranges suggested here at tfp.
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    Re: Should TDS be part of the 'PoolMath' ?

    Quote Originally Posted by oldguy70 View Post
    Even without a SWG, I should at least check my salt level (have been guessing based on chlorine used) and if the minimum assumption is that I added calcium chloride the PoolMath may be a tad off for myself.
    I'm pretty sure that unless you have added salt to your pool water, then the amount (of salt) added from bleach/liquid chlorine will be very low unless you have had the same water in your pool for a very long time [read: many years, possibly decades]. That would mean the same water with no dilution or replacement, except to make up for evaporation, since that results in a net change of zero as far as salt.

    That would mean there's no real reason to test for salt levels... Although if you are really concerned, it is a test the pool store can do. Just tell them you need your salt level checked. Then when they tell you it's low, just smile & nod, and thank them kindly. You could wait until you need something from there anyway, if you're afraid you'll want to buy something.


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    Re: Should TDS be part of the 'PoolMath' ?

    Quote Originally Posted by duraleigh View Post
    Chem geek and I disagree on the importance of csi. I simply cannot argue the technical merits but, from a practical standpoint, I can say that thousands upon thousand upon thousands of pools stay swimmable and crystal clear and do not have calcium scale issues and their pool water managers NEVER calculate csi.

    I do not have the background to understand it's precise importance but I know for the large majority of us, we do not need to be concerned with csi as long as the parameters we test for are kept within the ranges suggested here at tfp.
    Well that simply isn't true because there IS calcium scaling in the SWG cells when the CSI gets even close to or higher than 0 (in the bulk pool water; obviously it's higher in the SWG cell at the hydrogen gas generation plate) which is why many target a slightly lower CSI (around -0.2) or use 50 ppm Borates. And it isn't true in spas where scaling (in plaster spas and in their heaters) has been seen at lower CSI such as +0.3. The statement you make with pools is only for plaster surface scaling where it is usually not seen until +0.7 or more.

    And then there's plaster degradation. That isn't something someone would see in just one year but over many years. Since the current Recommended Levels for plaster SWG pools has the low-end of those ranges down to -0.56 which has a calcium carbonate level only 28% of that at full saturation that protects plaster surfaces, then why bother with any calcium in the pool at all? Any pool? Just ignore the science of calcium carbonate saturation to protect plaster pool surfaces completely. Are we going to wait and see what happens in pools where some smaller percentage are following the Recommended Levels but on the low end of everything except CYA at the high end?

    onBalance will be doing some experiments to get more definitive data on low CSI degradation rates and specifically low CH vs. low TA (his earlier experiments showed SERIOUS calcium removal during the first month of plaster curing in water under-saturated with calcium carbonate but much less thereafter and this was at the -0.6 or -0.7 range we are talking about), but in the meantime why risk pools by having a recommendation for pool water which at one extreme has only one-fourth the needed amount of calcium carbonate in the water? We most definitely do not have enough data to disregard saturating pools with calcium carbonate to protect their plaster surfaces over 15 or more years of expected plaster life.
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