You have to know what you are doing. The addition of muriatic acid lowers the pH and total alkalinity in Swimming Pools.
The water becomes aggressive and can etch the plaster and metal parts of the pool and equipment.
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.
To increase the chlorine level in a swimming pool, you can add chlorine tablets, liquid chlorine, or granular chlorine according to the manufacturer's instructions based on the pool's size and the current chlorine level. It's important to regularly test the water to ensure the chlorine level is within the recommended range for safe swimming.
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To adjust pH and/or lower alkalinity.
'Swimming Pool', sometimes shortened to 'Pool'.
Remove some of the water and refill it with fresh water.
add a PH reducer chemical
A cork has a low density. It is lower then water. That causes it to float.
Using sodium bicarbonate to lower pH in a swimming pool is not effective. Sodium bicarbonate, or baking soda, is typically used to raise pH levels in pools. To lower pH in a pool, an acid such as muriatic acid or sodium bisulfate should be used.
What are swimming pool "Coopers"
it depends on which swimming pool