Liquid bleach vs. Total Dissolved Solids?

[chem geek]

Carl is absolutely right. [EDIT] Well, no, I was wrong because I didn't account for the salt that is in liquid chlorine due to its production from chlorine gas into a solution of lye (caustic soda). I have corrected the TDS amount below. 12.5% chlorinating liquid is around 125,000 ppm chlorine and around 100,000 ppm salt making it about 3 times saltier than sea water (359,000 ppm is saturated salt water or brine). [END-EDIT] The following table shows the increase in TDS, calcium, and other factors. The TDS is calculated after the chlorine that is added gets consumed (chlorine consumption is an acidic process) and after any base is added (if necessary) to restore pH (the base used is caustic soda -- other bases increase TDS for Trichlor and Dichlor even more).

Increase in TDS, Calcium and CYA with 1 ppm FC increase and usage

Type of Chlorine          TDS  CH   CYA  Acid/Base
Bleach / Liquid Chlorine  1.6  0.0  0.0  Slightly Basic
SWG                       0.0  0.0  0.0  Neutral to Moderately Basic*
Calcium Hypochlorite      1.2  0.7  0.0  Slightly Basic
Trichlor (tablets)        1.4  0.0  0.6  Very Acidic
Dichlor (granular)        1.8  0.0  0.9  Moderately Acidic
Chlorine Gas              1.6  0.0  0.0  Extremely Acidic

*SWG varies in its tendency to increase pH and therefore the amount of acid needed to remain neutral. The pH rise (probably from outgassing carbon dioxide due to aeration from the hydrogen bubbles created in the SWG) and added acid to restore pH will increase TDS, but is not shown above since it varies by pool.

In a salt-water pool using an SWG, the TDS is already high due to the added salt. By using bleach or liquid chlorine you will be adding the smallest amount of TDS and will not increase CH nor CYA and will probably not need to add any acid or base. [EDIT] This is not true because I did not account for the salt that is in the liquid chlorine originally. [END-EDIT] During the winter with cold pool water temperatures, you will be adding very little chlorine, perhaps only 1-2 ppm FC per week (if that much) which means that you will be adding 1.6 ppm [EDIT] NO! actually it's 3.2 ppm [END-EDIT] or less TDS per week or adding only 32 ppm TDS [EDIT] NO! it's 64 ppm TDS [END-EDIT] over 20 weeks. This TDS is actually just salt so is exactly the same as if you added 32 ppm salt to your pool. This is only a 1% increase [EDIT] NO! it's a 2% increase [END-EDIT] in your salt level and you probably will lose at least that much through dilution/overflow.

Richard