I made a mistake, usually it is potassium chloride.

https://www.amazon.com/NoSalt-Sodium-Free-Salt-Alternative-Ounce/dp/B0183RU7VI

https://www.amazon.com/BulkSupplements-Potassium-Chloride-Powder-Kilogram/dp/B00ENS39XK/

https://www.amazon.com/Nutricost-Potassium-Chloride-Powder-1kg/dp/B097X3QW99/

Windsor salt free salt substitute is another one but isn’t on amazon.com.

Check out the wiki page for Electrolytes

Any premixed isn't going to give you enough and will be criminally expensive. Please check the wiki, you need way more electrolytes than you think you do.

Personally I do this:

For electrolytes I have a 2L water bottle that I mix each morning with

• 2 L water
• 13 g Morton Pink Salt (which gives 5g sodium)
• 11 g NoSalt (which gives 4g potassium)

I have 24oz insulated Bubba tumbler w/ straw that I use to do the actual drinking and I recently started adding Great Value brand Fruit Punch drink mix which makes it so much easier to insure I drink all of it.

Then I just use a regular magnesium supplement.

Yes rice flour would break your fast.

Have you tried adding some mio type stuff to the water? I mix my electrolytes in a pretty heavy concentration (13g salt + 11g nosalt + 2L water) and struggled to drink it all, I started adding some fruit punch drink enhancer and I swear I can't even taste the saltiness anymore, it's crazy how well it worked.

edit: To clear the numbers up:

• 13g of salt (table salt, pink salt, etc) contains 5g *sodium*, which is about what you need per day
  
• 11g of nosalt (potassium salt substitute) contains 4g *potassium*, which is about what you need per day

edit2: Just gonna copy paste the whole thing I have;

For electrolytes I have a 2L water bottle that I mix each morning with

• 2 L water
  
• 13 g Morton Pink Salt (which gives 5g sodium)
  
• 11 g NoSalt (which gives 4g potassium)
  

I have 24oz insulated Bubba tumbler w/ straw that I use to do the actual drinking and I recently started adding Great Value brand Fruit Punch drink mix which makes it so much easier to insure I drink all of it.