to convert hard water in to soft water

calcium sulfite for removing clorine from water but it makes water hard water.. 

Polyphosphate Siliphos Balls are used for conditioning water so that it wont scale.. 

sodium gluconate and sodium bicorbonate for chilating or for softening water...

sodium polyphosphate commonly called sodium hexametaphosphate (SHMP).. 

It's also known as sodium polymetaphosphate and soluble sodium metaphosphate glass.  SILIPHOS

this is mainly usedin ROs also food grade

https://www.quora.com/Do-water-softening-shower-heads-work-or-do-they-just-replace-what-they-pick-out-with-sodium

lime (calcium hydroxide) and soda ash (sodium carbonate) vs SHMP

While both lime (calcium hydroxide) and soda ash (sodium carbonate) are primarily used for water softening through precipitation by raising pH and causing calcium and magnesium ions to precipitate out, SHMP (sodium hexametaphosphate) functions as a chelating agent, meaning it "wraps around" calcium ions, effectively softening water without precipitation, making it a different mechanism of action compared to the lime-soda ash combination. 

https://aguapuro.com/water-softener/

they supply automated mixing and chemical addng with PH balance machines 

Key differences: 

• Function:

  Lime and soda ash work by raising pH to precipitate calcium and magnesium ions as insoluble carbonates and hydroxides, while SHMP "sequesters" calcium ions by forming a complex with them, preventing them from reacting with other substances. 
• Application:

  Lime and soda ash are commonly used in large-scale water softening processes, while SHMP finds applications in smaller scale water treatment, food processing (as a quality improver), and industrial processes due to its ability to prevent mineral deposition. 
• Chemical reaction:

  When added to water, lime and soda ash react to form insoluble precipitates, while SHMP dissolves and forms a complex with calcium ions without visible precipitation. 

Sodium hexametaphosphate (SHMP) has been widely used in ceramics, refractories, detergents and other industries from the beginning of Water Treatment to overcome the "red water" phenomenon. It is also an important industrial raw material for water treatment. It is easily soluble in water and the aqueous solution is alkaline. The pH of 1% sodium hexametaphosphate aqueous solution is 9.7, and it is hydrolyzed into phosphite gradually in water. It has good ability of complexing metal ions with calcium and magnesium Metal ions such as iron and iron are complexed to form soluble complex, which can soften hard water, reduce the amount of detergent used in washing and increase the cleanliness of clothes.

 

https://www.jinhetec.com/blog/the-use-of-sodium-hexametaphosphate-is-also-a-key-factor-affecting-the-washing-effect-24997.html

they also sell in bulk from china..

health issues of SHMP

https://pubmed.ncbi.nlm.nih.gov/11766135/