TDS

[Guest]

Waterbear,

So if what your saying is correct... I could have a pool with a TDS of 8000ppm that will be just as easy to maintain, as a pool with a TDS of 800ppm?? I know for a fact the pool with 8000ppm will require more MA and Chlorine than the pool with a TDS of 800pm. Like I said "each pool will be different based on many of variables. We serviced a pool that had a TDS of over 6000ppm and it required 14 gallons of chlorine and 9 gallons of acid a month. After lowering the TDS below 500ppm, this pool only required 1-2 gallons of chlorine a month and 1/2 gallon of acid a month.

 

[JasonLion]

Re: CYA above 40 is too high

TDS is essentially useless because it doesn't tell you what is actually in the water. It is completely possible to have a pool with a TDS reading of over 35,000 and have the water be perfectly well behaved, and have another pool with TDS around 1,000 that is completely intractable. TDS alone doesn't tell you anything.

Salt can raise TDS dramatically without causing any problems. An ocean water pool will routinely have TDS numbers over 30,000. Meanwhile, 500 ppm of CYA, or 5 ppm of ammonia, or 500 ppm of TA, or 500 ppm of borates can raise TDS just a little and cause huge problems. It all depends on what, specifically, is actually in the water.

 

[Guest]

Re: CYA above 40 is too high

Exactly... Each pool is different!

 

[ideliver]

Re: CYA above 40 is too high

:: ::

How did I miss this thread...

 

[JasonLion]

Re: CYA above 40 is too high

Exactly... Each pool is different!

Right. And therefore what you said originally is either wrong or misleading.

I could have a pool with a TDS of 8000ppm that will be just as easy to maintain, as a pool with a TDS of 800ppm??

Yes, it absolutely could happen.

I know for a fact the pool with 8000ppm will require more MA and Chlorine than the pool with a TDS of 800pm.

No, only sometimes. Some pool with a TDS reading of 8000 ppm will require exactly the same amount of MA and Chlorine as some pool with a TDS of 800pm. You need to know more about the pool, have they been using salt, what are the individual levels, before you make judgments like this one. Higher MA and/or Chlorine demand are common with some causes of high TDS and quite rare with other causes of high TDS. If all you know is the TDS reading then you can't make this statement.

 

[Guest]

Re: CYA above 40 is too high

What if the CH was about 1500ppm (out of the 8000ppm TDS) Would that require more acid and chlorine? If we remove the CH and drop it to 250ppm all other dissolved solids to below below 500ppm (Non SWG'ing pool). Lowering the TDS regardless is going to make it easier to maintain any pool. You will use less chemicals. We just did a pool in the Phoenix area and I describe my results in the last post.

 

[Guest]

Re: CYA above 40 is too high

Exactly... Each pool is different!

Right and it's not the TDS that matters but the actual ionic species present. I explained how TDS got it's bad rap historically as a proxy for CYA levels with pools running stabilized chlorine and this has stuck as strongly in the industry as the 'slug method' for lowering TA (Acid column) which we all know (or should know) has been scientifically disproven by Kim Skinner and J. Que Hales of Pool Chlor! Here is a link to their paper that was publised in the JSPSI (Journal of the Pool and Spa Industry)
http://www.poolhelp.com/JSPSI_V1N2_16-30_AcidColumn.pdf

The photographs at the end of the paper that show how MA puddles when added to still water are really amazing and shows without a doubt how harmful slugging acid it to pool surfaces!

It is just another one of those "things everyone knows that aren't true" as Ben Powell from Pool Forum liked to call them, just like TDS being of any value as a water measurement to determine water quality!
TDS is a useful measurement for determining the CSI but that's about it!

 

[Guest]

Re: CYA above 40 is too high

We just did a pool in the Phoenix area and I describe my results in the last post.

Are you, by any chance, in the industry?

 

[Guest]

Re: CYA above 40 is too high

Lowering the TDS regardless is going to make it easier to maintain any pool. You will use less chemicals.

Blatently untrue! If you have a pool with a TDS of 600 ppm and add 4000 ppm salt you will have absolutely no effect on the amount of MA needed to lower the pH or TA not will it have any effedt on the amount of chlorine needed to raise FC by a given amount. However, if you take the same pool with 600 ppm TDS and add 400 ppm of bicarbonate to it your total TDS is going to be far lower than the first example but, since you have now extremely overcarbonated this pool you will increase the acid demand in this pool significantly but is not going to impact chlorine usage. If you lower the TA by the addition of either MA or bisulfite you will increase TDS even more by the addition of sodium ion, and either chloride or sulfate ions but the acid demand in the pool will actually decrease!
TDS on it's own tells us nothing here. The fact that the second example the TA was raised by a very large amount (for TA) which had minimal impact on TDS had a far greater impact on water chemistry. TDS, as it is commonly used by the industry, is a bogus measurement!

 

[chem geek]

Re: CYA above 40 is too high

So if what your saying is correct... I could have a pool with a TDS of 8000ppm that will be just as easy to maintain, as a pool with a TDS of 800ppm?? I know for a fact the pool with 8000ppm will require more MA and Chlorine than the pool with a TDS of 800pm. Like I said "each pool will be different based on many of variables. We serviced a pool that had a TDS of over 6000ppm and it required 14 gallons of chlorine and 9 gallons of acid a month. After lowering the TDS below 500ppm, this pool only required 1-2 gallons of chlorine a month and 1/2 gallon of acid a month.

If the pool with high TDS had a high CYA level, then it could be consuming much more chlorine because the chlorine is far less effective so unless the FC was raised much higher, then algae growth could occur leading to a much higher chlorine consumption. I had that happen in my own pool 6 years ago after using Trichlor pucks when my usual 0.8 ppm FC per day (with a pool cover on except for 1-2 hours on some days) turned into double or triple that chlorine demand when my CYA hit 150 ppm -- and that was using PolyQuat 60 algaecide, but only every other week. The algae wasn't visible when this chlorine demand was higher, though eventually the water started to turn dull.

If in the high TDS pool the TA was higher, then that can lead to more carbon dioxide outgassing which causes the pH to rise requiring more acid to compensate for that.

So as others have been saying, it is the composition of TDS that is important, not the TDS itself. TDS is usually mostly salt. However, a higher TDS in a pool can reflect the "age" of the water since continued chlorine use does result in salt buildup if there isn't sufficient dilution. So other organics and substances can build up in the pool as well and these can eventually result in a higher chlorine demand if they are slower to oxidize. However, you can't just look at TDS alone as a single indicator since it can be high just with salt or it can be high in TA or CYA which have side effects or it can be filled with other substances that aren't measured, etc.

In your later post example with very high CH, that is a risk for scaling if the pH and TA are a bit high.

So no one is saying that after everything else is looked at that one shouldn't consider water replacement as a solution to a problem. It's just that high TDS by itself doesn't mean very much. Look at everything else first for a more specific explanation and solution.

Richard

 

[Guest]

We serviced a pool that had a TDS of over 6000ppm and it required 14 gallons of chlorine and 9 gallons of acid a month. After lowering the TDS below 500ppm, this pool only required 1-2 gallons of chlorine a month and 1/2 gallon of acid a month.

Waterbear, can you explain this? (I get it... TDS is a makeup of many things) Explain why this pool used less chemicals after lowering TDS (everything in the water).
I could explain it if you gave me before and after water test results. I assume the
TDS was lowered by straight dilution and not by some of the proprietary methods of CH reduction that are out there?

Like I said TDS by itself is a bogus measurement that tells us nothing. If you give me a full set of test results I can tell you what is going on in a pool. If you give me a history of test resuls I could do even better but a before and after the dilution woud be enough to know what actually changed (although I would guess CYA and TA to be the main players in this scenario!)

 

[JasonLion]

If you had a complete set of water test results I am sure we could tell you exactly what was happening. Taking a random guess, I would assume that the TA level was way too high before, and much more reasonable after, thus the acid difference.

The chlorine amounts you quote are simply impossible, no pool will ever use as little as 2 gallons of chlorine in a month, unless it is a six foot wading pool.

 

[Guest]

If you had a complete set of water test results I am sure we could tell you exactly what was happening. Taking a random guess, I would assume that the TA level was way too high before, and much more reasonable after, thus the acid difference.

The chlorine amounts you quote are simply impossible, no pool will ever use as little as 2 gallons of chlorine in a month, unless it is a six foot wading pool.

Jason,

Since, you insist that I lied (bold), theres no reason to continue this thread.

 

[chem geek]

salp,

Please don't take it that way. The lowest daily chlorine usage rates we've seen even with high CYA levels are at least 1 ppm FC per day for a pool exposed to sunlight and usually it's higher than that. That would be 30 ppm FC per month. Two gallons of 12.5% chlorinating liquid in 8300 gallons would be 30 ppm FC. That's why Jason found your statement surprising, but it's not impossible if you are talking about a smaller pool or a pool not exposed to sunlight nor a high bather load or a pool with some other form of oxidation (say, non-chlorine shock) or where the water is cool.

Would you please tell us more details about the pool that only required 1-2 gallons of chlorine per month? For example, the pool's size in gallons, whether it is exposed to full sun during the day (or is covered), the temperature of the water, if there was any supplemental oxidizer being used such as non-chlorine shock, and the pool's normal FC and CYA levels?

Richard

 

[Guest]

We serviced a pool that had a TDS of over 6000ppm and it required 14 gallons of chlorine and 9 gallons of acid a month. After lowering the TDS below 500ppm, this pool only required 1-2 gallons of chlorine a month and 1/2 gallon of acid a month.

Waterbear, can you explain this? (I get it... TDS is a makeup of many things) Explain why this pool used less chemicals after lowering TDS (everything in the water).

As jason said, this is bogus if liquid chlorine was the only source of chlorne unless this was a VERY TINY pool!

 

[Guest]

If you had a complete set of water test results I am sure we could tell you exactly what was happening. Taking a random guess, I would assume that the TA level was way too high before, and much more reasonable after, thus the acid difference.

The chlorine amounts you quote are simply impossible, no pool will ever use as little as 2 gallons of chlorine in a month, unless it is a six foot wading pool.

Jason,

Since, you insist that I lied (bold), theres no reason to continue this thread.

No one said you lied. How many gallons is the pool? An average 10k pool that only loses 1ppm FC daily (and that is not a common scenario at all) will consume over 2 gallons a month (closer to 2 1/3) and since a more 'average' daily FC loss is 2-3 ppm the amount of chlorine used will be in the neighborhod of 5-7 gallons a month. Even if we look at a very small 5K pool you are looking at between about 2.5 to 3.5 ga of 12.5% liquid chlorine a month. Also, the amount of chlorine used is also dependant on the CYA level.

Once again, I ask you if you are in the industry and exactly what do you do (it's pretty obvious that you are in the industry but I am going to guess that you are in sales since you just seem to be learning about water maintenance and don't quite have the chemistry down. You have to remember that some of us on here come from a background of chemistry before we got into pools so sometimes things that are obvious to us need to be fully explained to others!