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This forum is a wealth of information and is a huge help to all of us pool owners. I ran across a great publication by the Missouri dept of health that would be a good reference for any of us.
http://www.dhss.mo.gov/RecreationalW...oolSpaChem.pdf
It speaks in fairly plain language and uses generic chemical terminology.
Unfortunately, the document also contains errors or misinformation that is common in the industry. There is no understanding of the relationship between chlorine and CYA -- specifically how CYA significantly lowers chlorine's effectiveness and requires higher FC levels at higher CYA levels to retain the same effectiveness. The document incorrectly states that chlorine's effectiveness is only reduced at very high CYA levels above 100 ppm. A Free Chlorine (FC) recommendation of 1.0 - 3.0 is given, independent of CYA level.
Most telling is the following statement that pretty much comes from the Pinellas study I talk about in this thread:
'Chlorine Lock,' a term given to a condition once thought to be produced from high cyanuric-acid levels tying up free available chlorine, has been proven false by the industry. Generally, high cyanuric acid levels of 400 ppm or higher are associated with excessive Total Dissolve Solids (TDS) or combined chlorine or chloramines and not "Chlorine Lock".
The misconception of hypochlorite forms of chlorine causing the pH to rise is also only half-true. When the chlorine gets used up, the pH drops so the net result is that such forms of chlorine are overall nearly pH neutral. The document states that Dichlor is nearly pH neutral, but again, after considering chlorine usage, it is actually acidic (though not as much as Trichlor).
There is a statement that "High TDS -- at 1,500 ppm above water-supply level -- can reduce chlorine efficiency by as much as 50%". That is not something I believe is supported by facts unless the TDS consists of too much CYA or similar compounds.
There is also the following statement:
Total dissolved solids have not received the attention they deserve for causing pool problems, because they aren’t easy to measure - and there’s a tendency to forget they’re in the water. Additionally, they’ve never received the kind of study and publicity that have surrounded cyanuric products. It has been proven that cyanuric acid causes no ill effects in pool water… but that it may, by it’s accumulation, signal the onset of problems due to TDS in the pool. Apparently this proof has been convincing, since the leading proponent of the overstabilization theory has built a cyanurate plant!
Those were just the most egregious errors that are counter to what we know and understand on this pool forum. It is unfortunate that such information continues to be perpetuated because the document does explain chemical concepts in a simple and easy to understand way.
Richard
Thank You, Richard!
Am I right in assuming that TDS include Sodium Chloride?
If so, then EVERY salt-water-generator pool has TDS levels far beyond the "recommended" levels.
After all, the pool industry claims that liquid chlorine/bleach adds lots more TDS than tri-chlor, di-chlor, or cal-hypo (all of which are solids that dissolve with binders that are not chlorine)...Are you as confused by this pretzel logic as I am?
Yes, TDS includes all salts, including sodium chloride. TDS is usually measured by a conductivity meter so in that context is measuring only charged chemical species (ions), but most of what is in pool water is charged species (except for the water itself, of course). The main exception is Boric Acid which mostly remains in pool water in its uncharged form so having Borates in the water doesn't show up in the TDS conductivity test. Also, the TDS from the conductivity test is an estimate where you have to make assumptions as to the components of that conductivity, so need to look at TA and CH and make adjustments (from tables) to do the test properly.
The other way to measure TDS is to boil off or evaporate all of the water and weigh the solids that are left. That also has its problems since it removes any volatile compounds from the water and specifically will drive off excess carbon dioxide lowering the TA part of TDS (measured TA itself doesn't change since it's just the pH that rises, but some of the bicarbonate weight will be lost by getting converted to carbon dioxide that gets outgassed).
So yes, every saltwater pool far exceeds the recommendations for TDS. As Evan and others have said, it's WHAT the TDS is composed of that is important, not its actual number. As for bleach/chlorinating liquid adding to TDS, Cal-Hypo add about as much salt as does Lithium Hypochlorite. It is true that Trichlor and Dichlor do not add "extra" salt so they result in half as much salt as the other forms of chlorine -- only the chlorine itself gets converted to salt (chloride) as it gets used up. The Trichlor and Dichlor have very little binders in them as far as I can tell, at least on a percentage basis. In terms of visible residue, it seems that Trichlor has a little and Cal-Hypo has more and I never notice any with Dichlor.
Richard
Once again, a wealth of information. It's easy for a layman like me to accept an "official government document" as fact. I thank you for chiming in Richard, even though much of it is greek to me:D