Breaking wash water means adding alkaline chemicals to tie up the calcium magnesium salts that make water hard. STPP is the most effective non-precipitating water softener in use. Bud in Texas wrote that during a heat wave the cold water was so warm that STPP had to be added to the initial flush to prevent blood in hospital linens from turning into stains.
Water softening is only part of reason for using "break" chemicals or cycle.
Breaking wash water means adding alkaline chemicals to tie up the calcium magnesium salts that make water hard. STPP is the most effective non-precipitating water softener in use. Bud in Texas wrote that during a heat wave the cold water was so warm that STPP had to be added to the initial flush to prevent blood in hospital linens from turning into stains.
Yes, you can "break" hard water by adding chemicals, this is why laundry break products contain water conditioners.
However, primary purpose (as have provided with links above) is to "break" heavy soils and fouling matter from textiles in preparation of main wash cycles and or in addition to same.
Raising pH of water causes textile (cotton, linen and other natural) to swell, that in turn causes them to open up and release soils trapped in or on whatever is being washed.
Alkaline conditions also cause saponifying of oils and fats on textiles which aids in their removal from wash.
Then, since and how you find same chemicals used for laundry break, sodium hydroxide/caustic soda, sodium metasilicate, sodium carbonate, ammonium hydroxide (in liquid form household ammonia)
https://www.alco-chem.com/uploads/7...lco_liquid_laundry_break_sds_2022-08-26_1.pdf
https://www.alco-chem.com/uploads/7...iquid_laundry_break_0275-cl5_fact_sheet_1.pdf
https://stppgroup.com/the-role-of-caustic-soda-in-enhancing-the-effectiveness-of-laundry-products-2
Sodium tripolyphosphate is a comparatively weak base substance with a pH value (in 1% solution) of 9.2~10.3
Sodium metasilicate is a stronger base: 1% solution has a pH of around 12.4 to 12.7.
Sodium carbonate: between 11 and 12 in 1% solution
For each movement up pH scale (or down) represents a 10x increase in alkalinity or acidity.
It's all relative to what one wishes to achieve.
Yes, STPP is great for softening hard water, but it also being a weak base on its own will not raise pH levels (in water solution) to cope with say heavy soil, muck and oily dirt.