Great online publication on pool health

[CarlD]

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?

[chem geek]

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

[shadowman]

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