If you fast forward to more recent times, the latest craze to handling the problems of CYA buildup making chlorine less effective (unless you proportionally raise the FC to keep the FC/CYA ratio constant) is the use of phosphate removers. These need to be seen in the same vein as algaecide in that they are not necessary if one maintains a minimum FC/CYA ratio, but since some pools are naturally low in phosphates while others have some one-time phosphate remover treatment done to them, there are pools that don't get algae in spite of the CYA level climbing pretty high. People who are not well-informed point to such pools as proof that what we teach is bogus, that the chlorine/CYA relationship isn't true, that high CYA is not a problem, etc.
So you need to keep in mind that the Chlorine/CYA Chart is based on minimum FC/CYA ratios that prevent green and black algae growth regardless of algae nutrient (phosphate, nitrate) level. It is NOT the minimum for any single pool. Some pools could target a lower level if their algae nutrients were lower (or if they were to use supplemental algaecide, such as Polyquat 60). We just simplify the recommendation to a single chart that covers virtually all pools (except those that get regularly introduced yellow/mustard algae). For advanced users who want a lower active chlorine level for whatever reason, they are welcome to pick the algae prevention technique of their choice and then target a lower FC/CYA ratio, but that is not common.
As for the pH and TA effects of various chlorine products, some of that info is described in the thread
Certified Pool Operator (CPO) training -- What is not taught where you can see that for every 10 ppm FC, Trichlor decreases TA by 7 ppm and Dichlor by 3.5 ppm. Basically, both are net acidic, but Trichlor about twice as much as Dichlor. So they consume TA and if you let the TA get too low then the pH can crash where it blows past a pH of 4.5 when the TA gets exhausted. This means that you HAVE to add some sort of pH or TA raising product when using either Trichlor or Dichlor and of course that increases the maintenance cost so should be figured in as is done in the thread
Cost Comparison of Chlorine Sources (though this data is somewhat dated, but the relative relationships are still roughly OK).
