tds bogus or true???????

[chem geek]

Regarding:

"TDS: Check it out when the water doesn't behave."
By David Dickman
Reprinted from Pool & Spa Service Industry News
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This is an excellent presentation of confusing information. [EDIT] No offense to RavenNS -- I'm referring to the article reprint only [END-EDIT]. To lump all TDS together is ridiculous. A sea water pool which has 30,000 to 40,000 TDS operates just fine so obviously it's not just high TDS that is the issue. When the TDS is composed mostly of simple salts, especially sodium and chloride, then this is not a problem (it does change water balance slightly, due to ionic strength). Most of the chemicals you add to your pool add sodium or chloride either immediately or when they get used up or broken down (i.e. chlorine). Carbonates that get added to your pool (sodium bicarbonate or sodium carbonate) do not build up because they are always outgassing as carbon dioxide to the air.

On the other hand, organic material that gets into the pool and gets partly broken down by chlorine can sometimes stick around and not completely decompose. If the material is large enough, then it will get caught in the filter. If not, then it will remain dissolved. Now some of this organic material, if broken down into smaller molecules, can become food for bacteria and algae so that may explain why some higher TDS situations lead to what appears to be a reduction in sanitation or algae prevention (but is actually just that you don't have enough chlorine in the first place and were lucky that conditions for faster bacterial or algae growth weren't present). However, a conservative amount of chlorine (i.e. Ben's chart) should still work reliably in that environment. So while it may be true that a low TDS pool may be able to get away with a somewhat lower level of chlorine (below the minimums in Ben's chart, for example), I wouldn't say that a high TDS pool isn't manageable.

As for the smell of water that is high in TDS and has not been changed in a spa, that is most likely the result of incomplete oxidation of organics and resulting chloramines (if chlorine is used as a sanitizer or if used in conjunction with bromine). It would be interesting to find out if shocking a spa with high chlorine levels would take care of this problem.

In spite of what I just said, I think that regularly changing spa water makes a lot of sense since the quantity of organic material and bad stuff that gets put into the water is much, much larger per volume of water in a spa compared to a pool (even a commercial pool). If anyone has figured out how to maintain and shock such water so that they don't have to change it (or change it infrequently), then that would be useful information to know. As for pools, I believe they can go a lot longer without a water change, but in general you would end up doing some change of your pool water over time anyway through backwashing DE or sand filters. If you have a cartridge filter, then you probably have to manually drain and refill some pool water to refresh it periodically. In my own pool (which has a cartridge filter due to water restrictions in my area), I let each winter's rains effectively change about a third or so of the pool water (accounting for "continuous dilution").

Richard

[Poolsean]

Sorry for the "sales pitch" but I mentioned that I would let you all know when a specific spa salt system was available...

AutoPilot has now introduced the Spa Pilot. Using 1500 ppm, it is designed to maintain a NON-USE chlorine residual for spas up to 800 gallons. It works in conjunction with "Power Pouches" that are added one pouch before and one after (potassium Monopersulfate and other propriatary ingredients).

[waterbear]

Poolsean, sounds like a winner to me! My spa is chlorinated by my SWG and it is really easy to maintain!

[waterbear]

RavenNS,
Since spas are drained and refilled every 1 to 3 months TDS is not an issue if they are properly maintained. The problem startes when people start dumping unnecessary defoamers, clairifies, fragrences, etc. into the water. Also, many people, including dealers, just don't understand bromine chemisty. Look at the number of people who just put bromine tabs in a floater and don't put sodum bromide in the water with each refill for an example and then wonder why they can't maintain a sanitizer level.....or the number of people who don't realize that chlorine is probably the most effective way to shock a bromine spa (or that almost all bromine tablets contain chlorine also for this reason!)

[chem geek]

Using 1500 ppm, it is designed to maintain a NON-USE chlorine residual for spas up to 800 gallons.

Sean,

Is the purpose of the chlorine primarily to regenerate bromide ion (Br-) back into hypobromous acid (HOBr) on a continual basis (which is what KMPS would do as well, though KMPS is also useful for oxidizing organics before chlorine does to prevent potentially smelly chloramine formation)? Or is it to also supplement the hypobromous acid for oxidation and disinfection? The "NON-USE" seems to imply that it is for the former, not the latter.

Richard

[RavenNS]

First of all, Chem Geek, absolutely no offense taken... I didn't write the article, I just thought it was worth reading (especially for newbies to TDS).
regarding adding chlorine to bromine: I thought we ( waterbear & chemgeek & I) discussed this as a bad idea in another thread lol

I dump the tub water about every three or four months, although timing can be quite important in winter... no one wants to do the empty-refill maintance in a blizzard.
I do use quite a bit of chemicals for start-up ( not just throwing some pucks in). I also have two chemicals for cleaning the filters which I do every month.
not to mention " tub clean" a very acidic chemical that you run through prior to draining.. ( eat your skin off! & so stinky too)

My primary hot tub, although outdoors, is essentially an almost "closed system". The cover is always on, unless we are in it... ( steam doesn't even escape it in the coldest days of winter). It is a completely independant system & this may make it "behave" differently than waterbear's tub which is part of his pool system.

I don't "shock" my tub per say ( except for start-up), but I do bring the levels up quickly ( & probably in-fact shocking it); We often throw some "bromoblast" in the tub as we get into it. We actually prefer to keep our tub at 10+ppm; this really helps my DH with some troubling skin conditions that he used to take medication for, prior to getting the Tub.
( and if you have any pus sores, the high bromine seems to draw out the infection & help the healing process as it dries out the sore & seems to close it up too.... Also cures diaper rash! lol... & strips my hair of colour beautifully.. )

As I said before I prefer the tub at a TDS of 800- 1000 ppm.I would be happy to just partially drain & refill, just to keep the TDS at that level.- I don't like the feel of high TDS water ( or low TDS water for that matter...lol). But I worry about the safety issues of residual bacteria living in the "pass-through" area of the motor/heater... ( I have a large amount of piping there... it may be like a tankless water heater, but it is several feet of piping)

( why is it difficult to believe that when there is tons of crap in your tub, or high TDS, that your sanitizer might get 'busy" with all that & that it won't be as effective? is it not plausibile?)

( also note that if you add fragrance for every tub-ride, you'll hit the high TDS mark very fast as well. & I suspect that the fragrance binding/bonding materials interfer somewhat with the sanitizers, although I have no proof of that. lol)

So maybe it isn't "important" if you are draining every three months... but for those people who don't; TDS monitoring is a good reminder of when to drain.

[chem geek]

( why is it difficult to believe that when there is tons of crap in your tub, or high TDS, that your sanitizer might get 'busy" with all that & that it won't be as effective? is it not plausibile?)

( also note that if you add fragrance for every tub-ride, you'll hit the high TDS mark very fast as well. & I suspect that the fragrance binding/bonding materials interfer somewhat with the sanitizers, although I have no proof of that. lol)

Normally dissolved substances, specifically charged ions, in water only interfere with chemical reactions due to what is known as "ionic strength". With sufficiently high TDS, this does in fact start to shift equilibrium towards charged ionic species since their "activity" is reduced relative to their actual concentration. My spreadsheet actually calculates all of this. However, the effect is very small in terms of its effect on chlorine concentration (though not on LSI or water balance) and essentially can be ignored for the ranges of TDS we are dealing with. It would be very important in sea water, but even salt SWCG pools do not have enough TDS to be of concern.

As an example, in a pool without CYA and with 2 ppm chlorine, 7.5 pH, 100 TA, 300 CH, 510 TDS (the minimum with these other parameters), and a temperature of 80F, this results in 0.968 HOCl (now correctly interpreted in ppm Cl2 units as all chlorine is measured due to historical convention). If I increase the TDS to 3500, then the HOCl drops to 0.909 which isn't a huge change.

Interestingly, if I repeat the above with CYA of 30 ppm and use 3 ppm chlorine, then I get at 525 TDS (again, the minimum which is higher due to the CYA), 0.042 for HOCl. If I increase the TDS to 3500, then the HOCl drops to 0.041 which is hardly a change at all.

The reason that changes in TDS have virtually no effect on HOCl in the presence of CYA is that the CYA acts like a chlorine (specifially an HOCl) buffer and resists changes in HOCl level due to outside factors. Specifically, the dominant equation where CYA buffers HOCl has charged ions of equal strength (charge) on both sides of the equation so changes in ionic strength due to TDS mostly cancel each other out. Without CYA, it is the HOCl/OCl- relationship that is affected and here there is charge on one side of the equation and no charge on the other.

Now in spite of what I just said it is of course possible that some forms of organics that get into the water may behave somewhat like CYA and tie up the chlorine and reduce its effectiveness. However, any such substance would have to also report its chlorine in the standard chlorine test for FC and would have to not be destroyed (oxidized) by the chlorine. Chlorine bound to CYA gets reported as FC since it is released from CYA in a matter of seconds. So yes, it is possible for some other organic compounds to behave in a similar fashion, but most are simply 1) combined with chlorine and stay that way as "combined chlorine" until fully oxidized (and are measured as the CC part of TC, but are not in FC) or 2) are not affected by chlorine at all. Obviously CYA is an "organic substance" that inhibits chlorine so certainly it is possible for other substances to behave this way as well.

So again, it is not the high TDS in and of itself that is a problem, but rather the fact that a high TDS may indicate older water that has more organics in it (in addition to salt) and some of these organics may interfere with chlorine's effectiveness. My hunch, however, is that for most standard organics that get into the pool or spa, that few if any inhibit chlorine's effectiveness (assuming you do not allow combined chlorine to build up since obviously that is chlorine that is not effective).

Richard

[KurtV]

( why is it difficult to believe that when there is tons of crap in your tub, or high TDS, that your sanitizer might get 'busy" with all that & that it won't be as effective? is it not plausibile?)

I guess the reason I find that hard to believe is that every pool with an SWG is operating at or above the "limit" of 3000 ppm. Most SWGs recommend something in the neighborhood of 3000 ppm of salt alone and some are designed to work at 6000 ppm and even higher. I've yet to hear from anyone with an SWG who didnt rave about it.

[Poolsean]

Richard,

It's primarily a chlorine generator but with additional NaCl and NaBr it can be a bromine generator. The "Non-Use" application means that the KMPS is used up front to create a residual for use, then to clean it up by oxidizing the combined chlorine (or combined bromine)...so actually, the latter.

[waterbear]

First of all, Chem Geek, absolutely no offense taken... I didn't write the article, I just thought it was worth reading (especially for newbies to TDS).
regarding adding chlorine to bromine: I thought we ( waterbear & chemgeek & I) discussed this as a bad idea in another thread lol
Wrong, I have stated many times that chlorine (read bleach) is probably the BEST oxidizer to use in a bromine system!
I dump the tub water about every three or four months, although timing can be quite important in winter... no one wants to do the empty-refill maintance in a blizzard.
I do use quite a bit of chemicals for start-up ( not just throwing some pucks in). I also have two chemicals for cleaning the filters which I do every month.
not to mention " tub clean" a very acidic chemical that you run through prior to draining.. ( eat your skin off! & so stinky too)
If you are so concerend about cleaning out the pipes I would suggest an enzyme product....they work great and are not toxic!
My primary hot tub, although outdoors, is essentially an almost "closed system". The cover is always on, unless we are in it... ( steam doesn't even escape it in the coldest days of winter). It is a completely independant system & this may make it "behave" differently than waterbear's tub which is part of his pool system.
I owned a portable hot tub for many years before I built my present pool/spa combo and kept it on both bromine and chlorine at different times.
I don't "shock" my tub per say ( except for start-up), but I do bring the levels up quickly ( & probably in-fact shocking it); We often throw some "bromoblast" in the tub as we get into it. We actually prefer to keep our tub at 10+ppm; this really helps my DH with some troubling skin conditions that he used to take medication for, prior to getting the Tub.
( and if you have any pus sores, the high bromine seems to draw out the infection & help the healing process as it dries out the sore & seems to close it up too.... Also cures diaper rash! lol... & strips my hair of colour beautifully.. )
Shocking is really a misnomer for a bromine system. When you add the oxidizer, whether chlorine, MPS, or ozone it reacts with the bromine ions in the water to form hypobromous acid....your active sanitizer. Tabs contain both bromine and chlorine or bromine and MPS so as they dissolve they add both to the water. If your bromine levels are low try adding some bleach and watch them shoot up (if you have a bromine reserve in the water) if you don't believe me!
As I said before I prefer the tub at a TDS of 800- 1000 ppm.I would be happy to just partially drain & refill, just to keep the TDS at that level.- I don't like the feel of high TDS water ( or low TDS water for that matter...lol). But I worry about the safety issues of residual bacteria living in the "pass-through" area of the motor/heater... ( I have a large amount of piping there... it may be like a tankless water heater, but it is several feet of piping)
and has a constant flow of water with residual sanitizer passing through it whenever the filtration system is running!
( why is it difficult to believe that when there is tons of crap in your tub, or high TDS, that your sanitizer might get 'busy" with all that & that it won't be as effective? is it not plausibile?)
because there is no chemisty to back it up!
( also note that if you add fragrance for every tub-ride, you'll hit the high TDS mark very fast as well. & I suspect that the fragrance binding/bonding materials interfer somewhat with the sanitizers, although I have no proof of that. lol)
do you really need that crap in your tub? It just means that you will have to drain your tub more often....and the ingredients probably won't show up on a TDS test. That measure ions in the water...non ionic additions to the water won't register on the test!
So maybe it isn't "important" if you are draining every three months... but for those people who don't; TDS monitoring is a good reminder of when to drain.

With both pools and hot tubs there are certain maintenace rules to follow if you want trouble free performance. With hot tubs it means draining and refilling on a regular basis. A good indication that you need to do this is when the tub starts to foam or you see heavy scum starting to collect on the water line