Remove some or all of the water
CaBr2.
Ca & P
CaHSO4.
Yes. Calcium is a metallic element.
they both have calicum
No one. There is no such word as calicum. Do you mean calcium? If so, it was discovered many years ago by scientists using scientific methods of examining bone tissue.
The only way to lower your cya level in your swimming pool is to partially drain your pool and fill with fresh water that will lower it or if you want to lower it to almost nothing completely drain your pool and start over but keep in mind chlorine tablets will raise your CYA level More information in the related link below.
alot
calcium is a metal "ca"
Add potash. See your pool shop with a sample of your water and the size of your pool and he will give you what your pool requires.
The only way to remove Hardness is to partially drain and refill your pool.
use something called soda ash you can find it at a pool or spa store