tds bogus or true???????

[waterbear]

Steve,
you are correct. ANY bromine based system needs sodium bromide in the water when the tub is initially filled. Tablets by themselves will NOT put enough bromine ions in the water to create a sufficient sanitizer level when the oxidiazer is added to the water for several weeks!
RavenNS, If sodium is the problems then Steve would get the same burns from either soft water or going into the ocean. I am sorry, but your theory does not 'hold water'....so to speak.

Once again I say TDS is a bogus measurement. In actual practice it means nothing. The main reason TDS came into use as a water parameter was NOT in bromine systems but in chlorine systems using stabilized chlorine. When trichlor and dichlor are used over a period of time TDS will rise (as it will with unstabilized chlorine) but so will the CYA (stabilziers). The vested intersts (manufacturers of stabilized chlorine and the pool stores that sell it) didn't want people to realize that the problems they were having with their pools was caused by the pools having too much CYA from continued use of stabilzied chlorine so TDS became the scapegoat and the reason they had to drain and refill. (Of course the problem is NOT our stabilzied chlorine tabs that you are using...its the TDS in the water! Your CYA level of 200 ppm is not the reason your chorine is not keeping the algae out of your pool...it's the TDS of 3000 ppm. It's not the high CYA that is causing the pitting of your plaster finish....it's the high TDS.) EVERY problems attributed to high TDS is KNOWN to be caused by overstabilization yet pools that have very high TDS (sometimes in excess of 6000 ppm) but are not overstabilized exhibit NONE of these problems....every pool with a SWG is a prime example!

Now if you would care to discuss the Langelier Saturation index (another bogus measurement)...

Also, bromine is a known sensitizer and many people have reactions from it. That is one of it's big downsides. I would like to know where you got the information that bromine helps skin coditions? If it is from the antibacterial effect then chlorine is equaly effective. In fact, chlorine is a more effective sanitizer than bromine. A FC level of 3 ppm is equivalent to a bromine level of 6.75 ppm!

[chem geek]

I would just like to respond to the earlier question about getting a TDS meter for home use. I suspect this isn't a great idea, though it's probably easier to get a reliable and relatively inexpensive TDS meter than it is to get an ORP sensor. TDS is most often measured by conductivity. This has several problems, however. First of all, it doesn't measure anything that isn't charged, so neutral dissolved solids aren't measured. Second, you have to plug in numbers into formulas for roughly what is already known to be in the water (CH, TA, etc.) since the conductivity measurement doesn't tell you the "weight" of the solid and "ppm" is a weight measurement. Finally, conductivity measurements are affected by the size of the charge, so an ion with a charge of 2 registers 4 times as much as an ion with a charge of 1 (a charge of 3 registers 9 times -- yes, it's the square of the charge that gets measured) so if you don't know what's in your water composing TDS, you're measurement will be bogus (probably too high).

So, bottom line, to the degree you already know a lot about what is in your pool or spa, then you have a chance of figuring out your TDS. The fact is that you can probably add it up yourself from the CH, TA, CYA, and salt (NaCl) (and maybe borates/boric acid if you use Borax). If you stick with BBB, then you won't have other junk including sulfates in your pool. Now with a hot tub that's using bromine and fragrances and all this other stuff, I personally think it's just better to change the water frequently regardless of TDS. As waterbear says, TDS is not particularly useful to know as a single total number -- it's the components that are important and there is no way of knowing if extra junk causing high TDS is a problem or not. If it's just plain salt, it's clearly not a problem.

I have TDS in my spreadsheet and it influences the boo-hoo'd saturation index (it's not so much that it's bogus, but that it's over-emphasized and I've improved upon it anyway ), but what is more useful is to know how much specific chloride ion there is, and sulfates, etc. since these influence things such as chlorine outgassing that are much more relevant and useful (though very hard to predict with accuracy).

Consider the following. If we can figure out why the pH rises in so many pools (both SWCG and non-SWCG) and can come up with something simple like keeping TA at 80 or 60 or something like that, then that will save a LOT on chemicals (acid) and will help keep down TDS as well.

Bottom line, save your money and try to focus on keeping things simple. Using BBB will significantly reduce the extra stuff that is in most pools -- clarifiers, KMPS shock (lots and lots of sulfate in that one), defoamers, enzymatic cleansers, sequestering agents, algicide, etc. etc.

Richard