tds bogus or true???????

[Simmons99]

If you are the only one with this spot and you don't get it anywhere else - are you sure it's something caused by the spa and not some other skin infection that is aggravated by the spa- (staph or strep infection comes to mind). I am not a doctor - just logically wondering why it would only affect you and then only one part of your body.

[RavenNS]

TRUE:

I've been a beachcomber hot tub, ( similar to arctic spas), owner for three years.
In my experience, yes TDS does matter.
When the TDS gets too high, your chemicals will not work as effectively, meaning you must use a lot more to effectively sanitize.
with conventional bromine or chlorine, after the sanitizer molecule burns up an organic particle, it turns into a bromamine or cloramine and thus leaves your hot tub with the cloudy, flat water ( if you have a lot of them... or high TDS).
it also can aid in making your hot tub have bad odor.

I'm not sure what the effect of a high TDS on your health might be...
( guess I should google it), but my guess would be that if your santizer isn't working as well then you leave yourself open for a multitude of possible health issues.

I would recommend taking your water to a different( brand) dealer of Hot Tubs for a free testing ( for comparrison purposes)...
I also suggest that you see your health professional.
( there is also a small possibility that you are allergic to bromine)

BTW, personally I prefer my "tub ride" at a TDS of about 800-1000... that's when everything just feels "right"... ( I find that "fresh water" doesn't bubble that well...lol)

The following is an article that I thought was interesting...
good luck with your tub

"TDS: Check it out when the water doesn't behave."
By David Dickman
Reprinted from Pool & Spa Service Industry News

TDS - Total Dissolved Solids - may be the most misunderstood factor in the whole field of pool & spa water chemistry. It is 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, algicides, 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.

Effect of Dissolved Material on TDS - Pools

(How Much 1 Pound of Material Will Raise TDS In Pools of Various Sizes)

Pool Capacity
TDS per 1 Pound

5,000 gal. 24 ppm
10,000 gal. 12 ppm
15,000 gal. 8 ppm
20,000 gal 6 ppm
25,000 gal 4.8 ppm
50,000 gal 2.4 ppm
100,000 gal 1.2 ppm
150,000 gal 0.8 ppm
Effect of Dissolved Material on TDS - Spas

(How Much 1 Pound of Material Will Raise TDS In Pools of Various Sizes)

Pool Capacity
TDS per 1 Pound

400 gal. 300 ppm
450 gal. 266 ppm
500 gal. 240 ppm
550 gal 218 ppm
600 gal 200 ppm
650 gal 184 ppm
700 gal 171 ppm
750 gal 160 ppm

The above charts should give you a pretty good idea of why TDS builds up so rapidly in spa water and also why the effect of chemical treatment is so dramatic when you are dealing with a spa. The accompanying charts - one for pools and the other for spas - will also give you an idea of how much of an impact 1 pound of chemical added to the water will have on TDS in vessels of different sizes.

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 additonal 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.

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, gggeenerally operate by either placing some water in a sample cell or dipping the meter directly in 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 deter mine the water's conductivity, the meter dial (or LCD readout) is calibrated to indicate TDS in parts per million.

The easieste way to reduce TDS is to drain the pool 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.

[turbottt1]

First simmons99 you have a valid point. When the old doc has seen my leg it's been in full bloom and is in fact a serious chemical burn. I've just about got it cleared up maybe I'll go have it checked now. steve

[chem geek]

Regarding:

"TDS: Check it out when the water doesn't behave."
By David Dickman
Reprinted from Pool & Spa Service Industry News
:
:
:

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