Add acid
You add water to the pool
No
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.
You can lower the PH level by using this stuff called PH Down. Go to a local pool store and ask about it.
Add potash or a similar product available from pool shops.
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
The side of the pool cover with bubbles is the lower side.
Remove some or all of the water
No